#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
typedef long long ll;
typedef pair<ll,int> P;
int N;
ll dp[2010][2010] = {};
ll A[2010],B[2010];
vector<P> v;
int main(){
    cin >> N;
    for(int i=1;i<=N;i++){
        cin >> A[i] >> B[i];
        v.push_back({B[i],i});
    }
    v.push_back(P(1e18,1e18));
    sort(v.begin(),v.end(),greater<P>());
    for(int i=0;i<=N;i++){
        for(int j=0;j<=N;j++){
            dp[i][j] = 1e18;
        }
    }
    for(int i=1;i<=N;i++){
        int id = v[i].second;
     //   cerr << B[id] << endl;
        for(int j=0;j<=N;j++){
            if(j==0) dp[i][j] = min(dp[i-1][j],A[id]);
            else dp[i][j] = min(min(dp[i][j],dp[i-1][j]),dp[i-1][j-1]+A[id]+j*B[id]);
        }
    }
    int day;
    day = N-N/3;
    /*for(int i=1;i<=N;i++){
        for(int j=0;j<=N;j++){
            cerr << dp[i][j] << " ";
        }
        cerr << endl;
    }
*/    cout << dp[N][day-1] << endl;
}