//#include <iostream>
#include <limits.h>
#include <fstream>
using namespace std;
const int NMAX = 5e4 + 1;
ifstream cin("energii.in");
ofstream cout("energii.out");
int n, W, dp[NMAX], w[NMAX], c[NMAX], minim = INT_MAX;
int main()
{
    cin >> n >> W;
    for (int i = 1; i <= n; i++)
    {
        cin >> w[i] >> c[i];
    }
    for (int i = 1; i < NMAX; i++)
    {
        dp[i] = INT_MAX;
    }
    for (int i = 1; i <= n; i++)
    {
        for (int g = 0; g <= W; g++)
        {
            if (dp[g] != INT_MAX)
            {
                dp[g + w[i]] = min(dp[g + w[i]], dp[g] + c[i]);

                if (g + w[i] >= W)
                {
                    minim = min(minim, dp[g + w[i]]);
                }
            }
        }
    }
    if (minim == 0)
    {
        cout << -1;
    }
    else
    {
        cout << minim;
    }
}