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

ifstream fin("energii.in");
ofstream fout("energii.out");

const int Dim = 1100;
const int MW  = 5100;
const int INF = 1 << 20;

int G,W,E,C,dp[Dim][MW];

inline int Min(int A,int B)
{
    return (A < B) ? A : B;
}

int main()
{
    fin >> G >> W;

    int i,j,ind;

    for (i = 0;i <= G;i++)
        for (j = 1;j <= W;j++)
             dp[i][j] = INF;

    for (i = 1;i <= G;i++)
    {
        fin >> E >> C;
        for (j = 0;j <= W;j++)
        {
            dp[i][j] = dp[i-1][j];

            if (j - E < 0) ind = 0;
                      else ind = j- E;

            dp[i][j] = Min(dp[i][j],dp[i-1][ind] + C);
        }
    }
    if (dp[G][W] == INF) fout << -1;
                    else fout << dp[G][W];
    return 0;
}