#include <fstream>
#define nmax 1005
using namespace std;
int e[nmax],c[nmax],dp[5005];
int main()
{
    int i,n,m,j;
    ifstream f ("energii.in");
    ofstream g ("energii.out");
    f>>n>>m;
    for (i=1;i<=n;i++)
        f>>e[i]>>c[i];
    for (i=0;i<=5000;i++) dp[i]=10000000;
    for (i=1;i<=n;i++)
        for (j=m;j>=1;j--)
            {
            if (j>e[i])
                dp[j]=min(dp[j],dp[j-e[i]]+c[i]);
            else
                dp[j]=min(dp[j],c[i]);
            }
    if (dp[m]!=10000000) g<<dp[m];
    else g<<-1;
}