#include <fstream>
#include <vector>

using namespace std;

const int INF = 1e9;

struct generator {
    int e, c;
};

int main() {
    ifstream in("energii.in");
    ofstream out("energii.out");
    int n, w;
    in >> n >> w;
    vector <generator> v(n);
    vector <int> cost(w + 1, INF);
    for (auto &g: v) {
        in >> g.e >> g.c;
    }
    in.close();
    cost[0] = 0;
    if (v[0].e <= w) {
        cost[v[0].e] = v[0].c;
    }
    for (int i = 1; i < n; i++) {
        for (int j = w - 1 + v[i].e; j >= v[i].e; j--) {
            if (cost[j-v[i].e] != INF) {
                int jj = j;
                if (jj > w) {
                    jj = w;
                }
                cost[jj] = min(cost[jj], cost[j-v[i].e] + v[i].c);
            }
        }
    }
    if (cost[w] == INF) {
        cost[w] = -1;
    }
    out << cost[w] << "\n";
    out.close();
    return 0;
}