#include <bits/stdc++.h>

using namespace std;
ifstream in("energii.in");
ofstream out("energii.out");
int e[1008],c[1008],dp[1009][80000];
#define INF 999999999
int main()
{
    long long g,w,nre=0;
    in>>g>>w;
    for(int i=1;i<=g;i++)
    {
        in>>e[i]>>c[i];
        nre+=e[i];
    }
    for(int i=0;i<=g;i++)
        for(int j=0;j<=nre;j++)
            dp[i][j]=INF;
    if(nre<w){out<<"-1";return 0;}
    for(int i=1;i<=g;i++)
        for(int j=0;j<=nre;j++)
    {dp[i][j]=min(dp[i-1][j],dp[i-1][j-e[i]]+c[i]);
     if(e[i]>=j)dp[i][j]=min(dp[i][j],c[i]);}
     out<<dp[g][w];

    return 0;
}