#include <bits/stdc++.h>

#define INF 0x3f3f3f3f

using namespace std;

int main() {
  ifstream cin("energii.in");
  ofstream cout("energii.out");

  int g, w;
  cin >> g >> w;

  vector<int> e(g), c(g);
  for (int i = 0; i < g; i++) {
    cin >> e[i] >> c[i];
  }

  vector<int> dp(w + 1, INF);
  dp[0] = 0;

  for (int i = 0; i < g; i++) {
    for (int j = w - e[i]; j < w; j++) {
      dp[w] = min(dp[w], dp[j] + c[i]);
    }

    for (int j = w - 1; j >= e[i]; j--) {
      dp[j] = min(dp[j], dp[j - e[i]] + c[i]);
    }
  }

  cout << (dp[w] != INF ? dp[w] : -1) << "\n";
  return 0;
}