#include <fstream>
#include <vector>

using namespace std;

int main()
{
    int nrGeneratoare, energiePornire, energie, cost;
    ifstream in("energii.in");
    ofstream out("energii.out");

    in >> nrGeneratoare >> energiePornire;
    vector<int> costDP(energiePornire + 1, 10005);

    for( int i = 0; i < nrGeneratoare; ++i )
    {
        in >> energie >> cost;
        for( int j = energiePornire; j >= 0; --j )
        {
            j<= energie ? costDP[j] = min(costDP[j], cost) : costDP[j] = min(costDP[j], costDP[j - energie] + cost);
        }
    }

    costDP[energiePornire] == 10005 ? out << -1 : out << costDP[energiePornire];

    in.close();
    out.close();
    return 0;
}