#include <fstream>

using namespace std;

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

const int gmax = 1000 , wmax = 5000;
int d[wmax + 1][gmax + 1] , e[gmax + 1] , c[gmax + 1];
int g , w;

int main()
{
    in >> g >> w;

    for(int i = 1 ; i <= g ; i++)
        in >> e[i] >> c[i];

    for(int i = 1 ; i <= w ; i++)
        d[i][0] = -1;

    for(int i = 1 ; i <= w ; i++)
        for(int j = 1 ; j <= g ; j++)
        {
            d[i][j] = -1;

            if(d[i][j - 1] != -1)
                d[i][j] = d[i][j - 1];

            if(i >= e[j] && d[i - e[j]][j - 1] != -1 && d[i][j] == -1)
                d[i][j] = d[i - e[j]][j - 1] + c[j];
            else if(i >= e[j] && d[i - e[j]][j - 1] != -1)
                d[i][j] = min(d[i][j] , d[i - e[j]][j - 1] + c[j]);
        }

    out << d[w][g] << '\n';
    return 0;
}