#include <fstream>
#define INF 0x3f3f3f3f
#define DIM 1005

using namespace std;

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

int G,E[DIM],C[DIM],W,D[5*DIM];
int main(){
    fin>>G>>W;
    for(int i=1;i<=G;i++)
        fin>>E[i]>>C[i];
    for(int i=1;i<=W;i++)
        D[i]=INF;
    for(int i=1;i<=G;i++)
        for(int j=G;j>=0;j--)
            if(D[j]!=INF){
                D[min(W,j+E[i])]=min(D[min(W,j+E[i])],D[j]+C[i]);
            }
    if(D[W]!=INF)
        fout<<D[W]<<"\n";
    else
        fout<<"-1\n";
    fin.close();fout.close();
    return 0;
}