#include <bits/stdc++.h>
using namespace std;

ifstream in("energii.in");
ofstream out("energii.out");

const int inf = 1e9;

int DP[2][5010];

int main() {
    ios::sync_with_stdio(false); in.tie(0); out.tie(0);

    int n, W; in >> n >> W;

    vector< pair< int, int > > centrale(n + 1);
    int maxSum = 0;
    for(int i = 1; i <= n; ++i) {
        in >> centrale[i].first >> centrale[i].second;
        maxSum += centrale[i].first;
    }

    if(maxSum < W) {
        out << "-1\n";
        exit(0);
    }

    for(int i = 0; i < 2; ++i) {
        for(int j = 0; j <= W + 1; ++j) {
            DP[i][j] = inf;
        }
    }

    for(int i = 1; i <= n; ++i) {
        for(int j = 0; j <= centrale[i].first; ++j) {
            DP[i % 2][j] = min(centrale[i].second, DP[abs(i % 2 - 1)][j]);
        }

        for(int j = centrale[i].first + 1; j <= W; ++j) {
            DP[i % 2][j] = min(DP[abs(i % 2 - 1)][j], centrale[i].second + DP[abs(i % 2 - 1)][j - centrale[i].first]);
        }
    }

    out << DP[n % 2][W] << "\n";

    in.close(); out.close();

    return 0;
}