#include <bits/stdc++.h>
using namespace std;
ifstream fin("energii.in");
ofstream fout("energii.out");

const int WMAX = 5005;
const int INF = 1e9;

int dp[WMAX + 1]; // cost minim pentru energia exactă j

int main() {
    int n, wmax;
    fin >> n >> wmax;

    fill(dp, dp + WMAX + 1, INF);
    dp[0] = 0;

    for(int i = 1; i <= n; i++) {
        int en, ct;
        fin >> en >> ct;
        for(int j = WMAX; j >= en; j--) { // 0/1 knapsack
            dp[j] = min(dp[j], dp[j - en] + ct);
        }
    }

    int ans = INF;
    for(int j = wmax; j <= WMAX; j++) {
        ans = min(ans, dp[j]);
    }

    fout << (ans == INF ? -1 : ans) << "\n";
    return 0;
}