#include <fstream>
using namespace std;
ifstream f ("energii.in");
ofstream g ("energii.out");
int n,k,c[5001],e,p,i,j,s,a;
int main()
{
    f>>n>>k; for(i=1;i<=k;++i) c[i]=2000000; for(i=1;i<=n;++i){f>>e>>p; for(j=k;j>=0;--j) if(j<=e)c[j]=min(c[j],p); else c[j]=min(c[j],c[j-e]+p);} if(c[k]!=2000000)g<<c[k]; else g<<"-1";
    return 0;
}