#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("energii.in");
ofstream fout("energii.out");
//G - numarul de generatoare
//W - cantitatea de energie necesara
//EG - cantitatea de energie produsa de generator
//CG - costul necesar producerii
int G, W, EG[1005], CG[1005];
int d[2][5005];
void citire() {
    fin >> G >> W;
    for (int i=1; i<=G; ++i) {
        fin >> EG[i] >> CG[i];
    }
}
int main()
{
    citire();
    for (int j=0; j<=W; ++j) {
        d[0][j]=999999;
    }
    d[1][W]=-1;
    for (int i=1; i<=G; ++i) {
        for (int j=EG[i]; j<=W; ++j) {
            d[1][j]=min(CG[i]+d[0][j-EG[i]], d[0][j]);
        }
        for (int j=0; j<=W; ++j) {
            d[0][j]=d[1][j];
        }
    }
    fout << d[1][W];
    return 0;
}