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

using namespace std;

long long dp[2001][2020];

void to(long long *x, long long y) {
  *x = min(*x, y);
}

int main() {
  int N;
  cin >> N;
  vector<long long> A(N);
  vector<long long> B(N);
  vector<int> P(N);
  for (int i = 0; i < N; i++) {
    cin >> A[i] >> B[i];
    P[i] = i;
  }
  sort(P.begin(), P.end(), [&](int i, int j) {
    return B[i] > B[j];
  });
  for (int i = 0; i <= N; i++) {
    for (int j = 0; j <= N; j++) {
      dp[i][j] = 1e18;
    }
  }
  dp[0][0] = 0;
  for (int i = 0; i < N; i++) {
    for (int j = 0; j <= N; j++) {
      long long c = A[P[i]] + B[P[i]] * j;
      to(&dp[i + 1][j], dp[i][j]);
      to(&dp[i + 1][j + 1], dp[i][j] + c);
    }
  }
  long long ans = 1e18;
  for (int j = 0; j <= N; j++) {
    int k = j / 2;
    if (j + k >= N) {
      ans = min(ans, dp[N][j]);
    }
  }
  cout << ans << endl;
}