#include <fstream>

using namespace std;

const int N = 5001;

int cost[N];

int main() {
    ifstream in("energii.in");
    ofstream out("energii.out");

    int n, w, e, c;
    in >> n >> w;
    for (int i = 1; i <= w; ++i)
        cost[i] = -1;
    while (n--) {
        in >> e >> c;
        for (int i = w - 1; i >= 0; --i)
            if (cost[i] >= 0) {
                if (cost[max(w, i + e)] == -1)
                    cost[max(w, i + e)] = cost[i] + c;
                else
                    cost[max(w, i + e)] = min(cost[i + e], cost[i] + c);
            }
    }
    if (cost[w] > 0)
        out << cost[w];
    else
        out << -1;

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