#include <fstream>

using namespace std;

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

int main()
{
    int G, W, E, C, i, j;
    int EGi[1001], CGi[1001];
    int Cmin[5001];

    cin >> G >> W;

    for (i = 1; i <= G; i++)
        cin >> EGi[i] >> CGi[i];

    for (i = 0; i <= W; i++)
        Cmin[i] = 10001;

    Cmin[0] = 0;

    for (i = 1; i <= G; i++)
        for (j = EGi[i]; j <= W; j++)
            if (Cmin[j - EGi[i]] + CGi[i] < Cmin[j])
                Cmin[j] = Cmin[j - EGi[i]] + CGi[i];

    if (Cmin[W] == 10001)
        cout << -1;
    else
        cout << Cmin[W];

    return 0;
}