#include <bits/stdc++.h>

using namespace std;
FILE * fi = fopen("energii.in", "r");
FILE * fo = fopen("energii.out", "w");
int g,w,e,c;
int lcurent=1;
int DP[2][5005];

int main()
{
    for(int j=1; j<=5001; j++)
        DP[0][j]=DP[1][j]=2000000000;
    fscanf(fi,"%d%d",&g,&w);
    for(int i=1; i<=g; i++)
    {
        fscanf(fi,"%d%d",&e,&c);
        for(int j=1; j<=e; j++)
            DP[lcurent][j]=min(c,DP[1-lcurent][j]);
        for(int j=e+1; j<=w; j++)
            DP[lcurent][j]=min(DP[1-lcurent][j],DP[1-lcurent][j-e]+c);
        lcurent=1-lcurent;
    }
    if(DP[1-lcurent][w]==2000000000)
        fprintf(fo,"%d",-1);
    else
        fprintf(fo,"%d",DP[1-lcurent][w]);
    fclose(fi);
    fclose(fo);
    return 0;
}