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#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <sstream>
#include <vector>

int main()
{
    std::ios_base::sync_with_stdio(0);

    int n, k, a;
    std::cin >> n >> k;
    std::vector<int> t(n + 1, 0);
    int m = 2020;
    for (int i = 1; i <= n; ++i) {
        for (int j = 1; j <= i; ++j) {
            std::cin >> a;
            t[j] += j;
            if (t[j] <= k && a < m) {
                m = a;
            }
        }
    }

    std::cout << m << std::endl;
    return 0;
}