#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <algorithm>
#include <vector>
#include <queue>
#include <stack>
#include <climits>
#include <string>
#include <set>
#include <cmath>
#include <map>
#include <unordered_map>
#include <numeric>
#include <random>
#include <memory>
#include <chrono>
#include <iterator>
#include <functional>
#ifdef LOCAL
#include "debug.h"
#else
#define debug(x...)
#endif
//#pragma GCC optimize("Ofast")

using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair <int, int> pii;
#define mp make_pair
#define pb push_back
#define sz(x) int((x).size())

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int N = 1e5 + 7;
const int inf = INT_MAX / 2;
const ll INF = LLONG_MAX / 3;
const int MOD = 998244353;
const ld eps = 1e-6;
const string cars[] = {"🚗", "🚕", "🚙"};


signed main() {
#ifdef LOCAL
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif
    cout << fixed << setprecision(3);
    cin.tie();
    cout.tie();

    ll n, ans = 0, c = 0;
    cin >> n;
    vector < pair < ll, ll > > a(n);
    vector < ll > p(n + 1);

    for (auto& [x, y] : a) {
        cin >> x >> y;
    }

    sort(a.begin(), a.end());

    for (int i = 0; i < n; i++) {
        p[i + 1] = p[i] + a[i].first;
    }
    debug(p);

    for (int i = n - 1; i >= 0; i--) {
        debug(a[i].first, p[i] + c);
        if (a[i].first >= p[i] + c) {
            ll x = ((a[i].first - (p[i] + c)) / 2 + 1);
            debug(x);
            ans += a[i].second * x;
            c += x;
        }
    }

    cout << ans;

    return 0;
}