#include <fstream>

using namespace std;

int g, w, i, j, e, c, a[5005];

int main () {
  ifstream fi("energii.in");
  ofstream fo("energii.out");
  fi >> g >> w;
  for (i = 1; i <= w; i++)
    a[i] = 2e9;
  for (i = 1; i <= g; i++) {
    fi >> e >> c;
    for (j = w; j >= 0; j--)
      if (j > e)
        a[j] = min(a[j], a[j-e]+c);
      else
        a[j] = min(a[j], c);
  }
  a[w] == 2e9 ? fo << -1 : fo << a[w];
  return 0;
}