#include <iostream>
#include <fstream>

using namespace std;

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

const int NMAX = 1001;
const int INF = 0x7fffffff;
const int WMAX = 5001;

int n, E;
int cant[NMAX], cost[NMAX];
int dp[WMAX][NMAX]; // costul minim pentru energia i si generatorul j

void citeste() {
    f >> n >> E;
    for (int i = 1; i <= n; i++)
        f >> cant[i] >> cost[i];
}

void rezolva() {
    for (int i = 0; i <= n; i++)
        for (int j = 0; j <= E; j++)
            dp[i][j] = INF;
    for (int i = 0; i <= n; i++) dp[i][0] = 0;

    for (int i = 1; i <= n; i++)
        for (int j = 0; j <= E; j++)
            if (j >= cant[i])
                dp[i][j] = min(dp[i - 1][j], dp[i][j - cant[i]] + cost[i]);
            else
                dp[i][j] = min(dp[i - 1][j], cost[i]);

    if (dp[n][E] == INF) {g << -1; return;}
    g << dp[n][E];
}

int main() {
    citeste();
    rezolva();
}