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#include <bits/stdc++.h>
#define endl '\n'
using namespace std;

int main () {
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	int n,k;
	cin >> n >> k;
	int wyn = 2020;
	int wino;
	for (int i=0;i<n;i++) {
		for (int j=0;j<i+1;j++) {
			cin >> wino;
			if (k >= (i+1-j)*(j+1)) {
				wyn = min(wyn,wino);
			}
		}
	}
	cout << wyn;
}