#include<iostream>
#include<vector>
#include<algorithm>

using namespace std;
using ll = long long;

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    int n;
    cin>>n;
    vector<ll> a(n),b(n);
    for(int i = 0;i<n;i++) cin>>a[i]>>b[i];

    int buy = 0;
    {
        int res = n;
        while(res>0){
            buy++;
            res--;
            if(buy%2==0) res--;
        }
    }
    vector<vector<ll>> dp(n+1,vector<ll>(buy+1,1e18));
    dp[0][0] = 0;
    vector<int> idx(n);
    for(int i = 0;i<n;i++) idx[i] = i;
    sort(idx.begin(),idx.end(),[&](int i,int j){
        return b[i] > b[j];
    });
    for(int i = 0;i<n;i++){
        for(int j = 0;j<=buy;j++){
            dp[i+1][j] = min(dp[i+1][j],dp[i][j]);
            if(j==buy) continue;
            int ni = idx[i];
            ll cost = a[ni] + j * b[ni];
            dp[i+1][j+1] = min(dp[i+1][j+1],dp[i][j]+cost);
        }
    }
    cout<<dp[n][buy]<<endl;
}