#include <iostream>
#include <fstream>
#include <vector>
#include <climits>
#include <algorithm>

using namespace std;

int main() {
    // Open input and output files
    ifstream fin("energii.in");
    ofstream fout("energii.out");

    int G, W;
    fin >> G >> W;

    // Initialize dp array where dp[i] will store the minimum cost to produce i units of energy.
    // Initialize with INT_MAX as it's impossible to produce any energy without generators.
    vector<int> dp(W + 1, INT_MAX); 

    // It costs 0 to produce 0 energy
    dp[0] = 0;

    // Read energy and cost for each generator
    for (int i = 0; i < G; ++i) {
        int E, C;
        fin >> E >> C;

        // Update the dp array
        for (int w = W; w >= 0; --w) {
            // If dp[w] is INT_MAX, we can't produce w energy, so skip
            if (dp[w] == INT_MAX) continue;

            // Otherwise, update dp for new energy level
            int new_w = w + E;
            if (new_w <= W) {
                dp[new_w] = min(dp[new_w], dp[w] + C);
            }
        }
    }

    // If it's possible to produce W energy, output the cost. Otherwise, output -1
    if (dp[W] == INT_MAX) {
        fout << "-1\n";
    } else {
        fout << dp[W] << "\n";
    }

    // Close files
    fin.close();
    fout.close();

    return 0;
}