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


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

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