#include <iostream>
#include <vector>
#include <limits>
#include <fstream>

using namespace std;

struct Generator {
    const int energy;
    const int cost;
};

int solve(const int req_energy, const vector<Generator> &generators) {
    const auto number_of_gen = generators.size();
    constexpr auto int_max = numeric_limits<int>::max();
    vector<vector<int>> cost_min(number_of_gen + 1, vector<int>(req_energy + 1, int_max));

    for (int i = 1; i <= req_energy; ++i)
        if (i <= generators[1].energy)
            cost_min[1][i] = generators[1].cost;

    for (auto i = 2; i <= generators.size(); ++i) {
        const auto generator = generators[i - 1];
        for (int energy = 1; energy <= req_energy; ++energy) {
            if (energy - generator.energy > 0) {
                cost_min[i][energy] = min(
                        cost_min[i - 1][energy],
                        cost_min[i - 1][energy - generator.energy] + generator.cost
                );
            } else {
                cost_min[i][energy] = min(cost_min[i - 1][energy], generator.cost);
            }
        }
    }

    return cost_min[number_of_gen][req_energy] == int_max ? -1 : cost_min[number_of_gen][req_energy];
}

int main() {

    ifstream in("energii.in");
    ifstream::sync_with_stdio(false);

    int G{};
    int W{};

    in >> G >> W;

    vector<Generator> generators{};
    for (int i = 0; i < G; i++) {
        int e{}, c{};
        in >> e >> c;
        generators.push_back({e, c});
    }

    ofstream out("energii.out");
    out << solve(W, generators);

    return 0;
}