#define _CRT_SECURE_NO_WARNINGS
#include "bits/stdc++.h"
using namespace std;
#define all(a) a.begin(), a.end()
#define int long long
const int inf = 1e18;
const int N = 1e5 + 100;
struct Line {
    int b, k, ind;
    Line(int _b, int _k) : b(_b), k(_k) {}
    Line(int _b, int _k, int ind_) : b(_b), k(_k), ind(ind_) {}
    Line() {
        b = 1e18;
        k = 0;
    }
    int get(int x) {
        return k * x + b;
    }
};
struct Node {
    Line v = { inf, 0 };
    Node* l = nullptr;
    Node* r = nullptr;
    Node* getl() {
        if (l == nullptr) {
            l = new Node();
        }
        return l;
    }
    Node* getr() {
        if (r == nullptr) {
            r = new Node();
        }
        return r;
    }
};
void update(Node* t, int tl, int tr, Line u) {
    int tm = (tl + tr) / 2;
    bool m = t->v.get(tm) > u.get(tm),
        l = t->v.get(tl) > u.get(tl);
    if (tl + 1 == tr) {
        return;
    }
    if (m) {
        swap(t->v, u);
    }
    if (m != l) {
        update(t->getl(), tl, tm, u);
    }
    else {
        update(t->getr(), tm, tr, u);
    }
}
void get_mn(Node* t, int tl, int tr, int x, int& res) {
    res = min(res, t->v.get(x));
    int tm = (tl + tr) / 2;
    if (x < tm) {
        if (t->l == nullptr) {
            return;
        }
        get_mn(t->l, tl, tm, x, res);
    }
    else {
        if (t->r == nullptr) {
            return;
        }
        get_mn(t->r, tm, tr, x, res);
    }
}
signed main() {
#ifdef _DEBUG
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    Node* dp[3][6];
    for (int i = 0; i < 3; i++) {
        for (int j = 0; j < 6; j++) {
            dp[i][j] = new Node();
        }
    }
    int n, ans = inf; cin >> n;
    for (int i = 0; i < n; i++) {
        int q, t; cin >> q >> t;
        int dp_now = (i == 0 ? 0 : inf);
        for (int t_f = 1; t_f <= 3; t_f++) {
            int x = i / (2 * t_f);
            get_mn(dp[t_f - 1][i % (2 * t_f)], -N, N, x, dp_now);
        }
        update(dp[t - 1][i % (2 * t)], -N, N, Line(-q * (i / (2 * t)) + dp_now, q));
        ans = min(ans, dp_now + q * ((n - i) / (2 * t) + 1));
        //cout << dp_now << '\n';
    }
    cout << ans;
}