#include <iostream>
#include <cstdio>

using namespace std;

int n, w, dp[5005];

struct generator{
    int en, ct;
}a[1005];

void citire(){
    cin >> n >> w;
    for(int i = 1; i <= n; i++)
        cin >> a[i].en >> a[i].ct;
    for(int i = 0; i <= 5005; ++i)
        dp[i] = 100000000;
}

int main()
{
    freopen("energii.in", "r", stdin);
    freopen("energii.out", "w", stdout);

    citire();

    for(int i = 1; i <= n; ++i)
        for(int j = w; j; --j)
            if(j <= a[i].en)
                dp[j] = min(dp[j], a[i].ct);
            else
                dp[j] = min(dp[j], a[i].ct + dp[j - a[i].en]);
    if(dp[w] >= 100000000)
        cout << -1;
    else
        cout << dp[w];
    return 0;
}