#include <bits/stdc++.h>
#define ll long long
#define ld long double
#define rep(i, r) for(int i = 0; i < (int)(r); i++)
#define reap(i, k, r) for(ll i = (ll)(k); i < (ll)(r); i++)
#define ALL(x) std::begin(x), std::end(x)
#define rALL(x) std::rbegin(x), std::rend(x)
#define MOD 998244353
using namespace std;
int main(){
    ll N; cin >> N;
    vector<ll> A(N), B(N);
    rep(i, N)cin >> A[i] >> B[i];
    ll use = 0;
    ll ans = 0;
    for(ll i = N - 1; i >= 0; i--){
        if(use * A[i] > B[i]){
            ans += use * A[i];
        }
        else{
            use++;
            ans += B[i];
        }
    }
    cout << ans << endl;
}