#include <iostream>
#include <fstream>
using namespace std;
ifstream f("energii.in");
ofstream g("energii.out");
int n, w, energie[1004], cost[1004], dp[5005];

int main()
{
    f >> n >> w;
    for(int i = 1; i <= n; i++)
        f >> 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] == 10005)
        g << -1;
    else
        g << dp[w];
    return 0;
}