#include <bits/stdc++.h>
using namespace std;

void chmin(int64_t& a, int64_t b){
    a = min(a, b);
}

int main(){
    int N;
    pair<int, int> BA[2000];
    cin >> N;
    for(int i=0; i<N; i++){
        int a, b;
        cin >> a >> b;
        BA[i] = {b, a};
    }
    sort(BA, BA+N, greater<>());

    int M = 0, get = 0;
    while(get < N){
        M++;
        get++;
        if(M % 2 == 0) get++;
    }

    const int64_t INF = 1e18;
    static int64_t dp[2010][2010];
    for(int i=0; i<=N; i++) for(int j=0; j<=N; j++) dp[i][j] = INF;
    dp[0][0] = 0;
    for(int i=0; i<N; i++){
        int b = BA[i].first, a = BA[i].second;
        for(int j=0; j<=M; j++){
            chmin(dp[i+1][j], dp[i][j]);
            if(j < M){
                int64_t result = dp[i][j] + a + b*j;
                chmin(dp[i+1][j+1], result);
            }
        }
    }

    cout << dp[N][M] << endl;
    return 0;
}