#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>
#include <vector>
#include <algorithm>
#include <set>
#include <map>
#include <cmath>
#include <ctime>
#include <functional>
#include <sstream>
#include <fstream>
#include <valarray>
#include <complex>
#include <queue>
#include <cassert>
#include <bitset>
using namespace std;

#ifdef LOCAL
    #define debug_flag 1
#else
    #define debug_flag 0
#endif

template <class T1, class T2 >
std::ostream& operator << (std::ostream& os, const pair<T1, T2> &p)
{
    os << "[" << p.first << ", " << p.second << "]";
    return os;
}

template <class T >
std::ostream& operator << (std::ostream& os, const std::vector<T>& v)
{
    os << "[";
    bool first = true;
    for (typename std::vector<T>::const_iterator it = v.begin(); it != v.end(); ++it)
    {
        if (!first)
            os << ", ";
        first = false;
        os << *it;
    }
    os << "]";
    return os;
}

#define dbg(args...) { if (debug_flag) { _print(_split(#args, ',').begin(), args); cerr << endl; } else { void(0);} }

vector<string> _split(const string& s, char c) {
    vector<string> v;
    stringstream ss(s);
    string x;
    while (getline(ss, x, c))
        v.emplace_back(x);
    return v;
}

void _print(vector<string>::iterator) {}
template<typename T, typename... Args>
void _print(vector<string>::iterator it, T a, Args... args) {
    string name = it -> substr((*it)[0] == ' ', it -> length());
    if (isalpha(name[0]))
        cerr << name  << " = " << a << " ";
    else
        cerr << name << " ";
    _print(++it, args...);
}

typedef long long int int64;

const int64 int64_INF = (int64)1e18;

namespace Slow
{
    int n;
    vector<int64> p_list;
    vector<int> d_list;

    int64 best_ans;

    set<vector<int64> > used;

    bool are_all_same(const vector<int> & l)
    {
        for (int i = 1; i < (int)l.size(); i++)
            if (l[0] != l[i])
                return false;
        return true;
    }

    vector<int64> get_state(int64 cur_ans, vector<int> colors, vector<int> cur_dist)
    {
        vector<int64> state;

        state.push_back(cur_ans);

        for (int64 x : colors)
            state.push_back(x);

        for (int64 x : cur_dist)
            state.push_back(x);

        return state;
    }

    void rec(int64 cur_ans, vector<int> colors, vector<int> cur_d_list)
    {
        if (cur_ans >= best_ans)
            return;

        vector<int64> state = get_state(cur_ans, colors, cur_d_list);

        if (used.count(state) == 1)
            return;

        used.insert(state);

        if (are_all_same(colors))
        {
            best_ans = min(best_ans, cur_ans);
            return;
        }

        for (int i = 0; i < n; i++)
        {
            for (int j = i + 1; j < n; j++)
            {
                if (colors[i] != colors[j] && cur_d_list[i] >= 1 && cur_d_list[j] >= 1)
                {
                    cur_d_list[i]--;
                    cur_d_list[j]--;

                    vector<int> new_colors = colors;
                    int x = colors[i];
                    int y = colors[j];

                    for (int & c : new_colors)
                        if (c == x)
                            c = y;

                    rec(cur_ans + abs(p_list[i] - p_list[j]), new_colors, cur_d_list);

                    cur_d_list[i]++;
                    cur_d_list[j]++;
                }
            }
        }
    }

    int64 solve(int _n, vector<int64> _p_list, vector<int> _d_list)
    {
        n = _n;
        p_list = _p_list;
        d_list = _d_list;

        best_ans = int64_INF;

        vector<int> colors(n);
        for (int i = 0; i < n; i++)
            colors[i] = i;

        rec(0, colors, d_list);

        if (best_ans == int64_INF)
            best_ans = -1;

        return best_ans;
    }

};

namespace Fast
{
    int n;
    vector<int64> p_list;
    vector<int> d_list;

    bool cmp_by_p(int a, int b)
    {
        return p_list[a] < p_list[b];
    }

    int64 get_dist(int a, int b)
    {
        return abs(p_list[a] - p_list[b]);
    }

    int64 solve(int _n, vector<int64> _p_list, vector<int> _d_list)
    {
        n = _n;
        p_list = _p_list;
        d_list = _d_list;

        if (n <= 2)
        {
            return Slow::solve(n, p_list, d_list);
        }

        vector<int> small_list;
        vector<int> big_list;

        for (int i = 0; i < n; i++)
        {
            if (d_list[i] == 1)
            {
                small_list.push_back(i);
            }
            else
            {
                big_list.push_back(i);
            }
        }

        int small_size = (int)small_list.size();
        int big_size = (int)big_list.size();

        sort(small_list.begin(), small_list.end(), cmp_by_p);
        sort(big_list.begin(), big_list.end(), cmp_by_p);

        if (big_size == 0)
            return -1;

        int64 ans0 = 0;

        for (int i = 0; i + 1 < big_size; i++)
        {
            int a = big_list[i];
            int b = big_list[i + 1];
            if (d_list[a] == 0 || d_list[b] == 0)
                return -1;
            d_list[a]--;
            d_list[b]--;
            ans0 += get_dist(a, b);
        }

        dbg(ans0);
        dbg(small_list);
        dbg(big_list);
        dbg("d_list after", d_list);

        vector<int64> dp(small_size + 1, int64_INF);
        dp[0] = 0;

        for (int i = 0; i < (int)big_list.size(); i++)
        {
            vector<int64> new_dp = dp;

            for (int j = 1; j <= small_size; j++)
            {
                int l = max(1, j - d_list[i] + 1);
                int r = j;

                int64 sum = 0;
                for (int t = r; t >= l; t--)
                {
                    sum += get_dist(big_list[i], small_list[t - 1]);
                    int64 cur_val = sum + dp[t - 1];
                    new_dp[j] = min(new_dp[j], cur_val);
                }
            }

            dp = new_dp;
        }

        int64 ans1 = dp[small_size];

        if (ans1 == int64_INF)
            return -1;

        return ans0 + ans1;
    }
};

void submit()
{
    int n;
    scanf("%d", &n);
    vector<int64> p_list(n);
    vector<int> d_list(n);
    for (int i = 0; i < n; i++)
    {
        scanf("%lld%d", &p_list[i], &d_list[i]);
    }

    int64 ans = Slow::solve(n, p_list, d_list);

    printf("%lld\n", ans);
}

void stress()
{
    const int IT = 1e5;

    const int N = 3;
    const int P = 3;
    const int D = 3;

    for (int it = 0; it < IT; it++)
    {
        printf("it = %d\n", it);

        int n = rand() % N + 1;
        vector<int64> p_list(n);
        vector<int> d_list(n);
        for (int i = 0; i < n; i++)
        {
            p_list[i] = rand() % P + 1;
            d_list[i] = rand() % D + 1;
        }

        int64 fast_ans = Fast::solve(n, p_list, d_list);
        int64 slow_ans = Slow::solve(n, p_list, d_list);

        if (fast_ans != slow_ans)
        {
            printf("fast_ans = %lld slow_ans = %lld\n", fast_ans, slow_ans);
            printf("%d\n", n);
            for (int i = 0; i < n; i++)
            {
                printf("%lld %d\n", p_list[i], d_list[i]);
            }
            return;
        }
    }

    printf("stress passed\n");
}

int main()
{
#ifdef LOCAL
    freopen ("input.txt", "r", stdin);
#endif

    submit();

    //stress();

    return 0;
}