#include <bits/stdc++.h>
#define nmax 22242423
using namespace std;


int n, k;

int v[5001];
int main()
{
    freopen("energii.in", "r", stdin);
    freopen("energii.out", "w", stdout);
int c, e;
    cin >> n;
    cin >> k;

    for(int i = 0; i <= k; i++)
        v[i] = nmax;

    for(int i = 1; i <= n; i++)
    {
        cin >> c >> e;

        for(int j = k; j >= 1; j--)
        {
          if(j == c)
          {
              v[j] = min(e, v[j]);
          }
          else if(j > c)
          {
              v[j] = min(v[j-c] +e, v[j]);
          }

        }
    }


    if(v[k] == nmax)
cout << -1;
else
    cout << v[k];


    return 0;
}