#include <bits/stdc++.h>
using namespace std;
using LL = long long;
int main(){
    int n;
    cin >> n;
    vector<int> a(n), b(n);
    for(int i = 0; i < n; i++) cin >> a[i] >> b[i];
    
    long long ans = 0;
    vector<vector<LL>> d(n, vector<LL>(n));
    for(int i = 0; i < n; i++){
        for(int j = 0; j < n; j++){
            d[i][j] = a[i] + b[i] * j;
            //cout << i << " " << j << " " << d[i][j] << endl;
            
        }
    }
    
    vector<bool> close(n, false);
    for(int i = n/2 + n%2 - 1; i >= 0; i--){
        int min_i = 0;
        for(int j = 0; j < n; j++) if(!close[j] && (d[j][i] != d[min_i][i] ? d[j][i] < d[min_i][i] : b[j] < b[min_i])) min_i = j;
        
        close[min_i] = true;
        ans += d[min_i][i];
    }
    cout << ans << endl;
}