#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
#define inf 100000000

using namespace std;

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

const int Nmax = 1005;

int main()
{
    int n, k, sum = 0;
    in >> n >> k;

    vector<int> dp(k + 1);
    vector<int> cost(n + 1);
    vector<int> energ(n + 1);

    for (int i = 1; i <= n; i++)
    {
        in >> energ[i] >> cost[i];
        sum = sum + energ[i];
    }

    for (int i = 1; i <= k; i++)
        dp[i] = inf;

    if (sum < k)
    {
        out << -1;
        return 0;
    }

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

    out << dp[k] << '\n';
    return 0;
}