#include <iostream>
#include <fstream>

using namespace std;

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

const int MAXN = 1004, MAXG = 10005;
int n, w, energie[MAXN], cost[MAXN], dp[5005];

int main()
{
    fin >> n >> w;
    for(int i = 1; i <= n; i++)
        fin >> energie[i] >> cost[i];
    for(int i = 0; i <= 5001; i++) dp[i] = 10005;
    for(int i = 1; i <= n; i++)
        for(int j = w; j; j--)
            if(j <= energie[i]) dp[j] = min(dp[j], cost[i]);
            else dp[j] = min(dp[j], dp[j-energie[i]] + cost[i]);
    if(dp[w] == MAXG) fout << -1;
    else fout << dp[w];
    return 0;
}