#include <fstream>
using namespace std;

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

int cost_minim[5001];

int main ()
{
    int generatoare , energie_necesara;
    cin >> generatoare >> energie_necesara;

    for (int indice = 1 ; indice <= energie_necesara ; indice++)
        cost_minim[indice] = 1e9;

    for (int indice = 1 , energie , cost ; indice <= generatoare ; indice++)
    {
        cin >> energie >> cost;

        for (int cantitate = energie ; cantitate <= energie_necesara ; cantitate++)
            cost_minim[cantitate] = min(cost_minim[cantitate] , cost_minim[cantitate - energie] + cost);
    }

    cout << (cost_minim[energie_necesara] == 1e9 ? -1 : cost_minim[energie_necesara]);
    cout.close(); cin.close();
    return 0;
}