#include <fstream>
#include <iostream>
#include <algorithm>
using namespace std;
const int NMAX = 5000, INF = 2e9;
int n, w, c[NMAX + 2], p[NMAX + 2], dp[NMAX + 2], i, j;
int main() {
    ifstream cin("energii.in");
    ofstream cout("energii.out");
    cin >> n >> w;
    for(i = 1; i <= n; ++i)
        cin >> p[i] >> c[i];
    for(j = 1; j <= w; j++)
        dp[j] = INF;
    for(i = 1; i <= n; ++i) {
        for(j = 0; j <= w; ++j) {
            if (j >= p[i]) {
                dp[j] = min(dp[j], dp[j - p[i]] + c[i]);
            }
        }
    }
    if(dp[w] == INF)
        cout << "-1\n";
    else
        cout << dp[w];
    return 0;
}