#include <fstream>
#include <iostream>
using namespace std;

ifstream f("energii.in");
ofstream fout("energii.out");
int main() {
    int g,w,eg[1002],cg[1002];
    int cost[1005][5005]; 
    f >> g >> w;

    for(int i = 1; i <= g; i++) {
        f >> eg[i] >> cg[i];
    }

    for(int i = 0; i <= g; i++) {
        for(int j = 0; j <= w; j++) 
            cost[i][j] = 100000;
    }

    for(int i = 1; i <= g; i++) {
        for(int j = 1; j <= w; j++) {
            
            if(j > eg[i]) {
                cost[i][j] = min(cost[i-1][j],cg[i] + cost[i-1][j - eg[i]]);
            }
            else {
                cost[i][j] = min(cost[i - 1][j],cg[i]);
            }
        }
    }

    int min = cost[g][w];
    if(min == 100000)
        fout << "-1";
    else
        fout << min;
    f.close();
    fout.close();
    return 0;

}