#include <iostream>

using namespace std;

int how_many_to_remove(const int& N, const int& w, const int& k)
{
	return N * (N + 1) / 2 - (k * (k + 1) / 2 +  (w - k - 1)*(w - k)/2 + (2*(w + 1) +(N - w - 1))*(N - w)/2);
}
int main()
{

	int n, k,a;
	a = 0;
	cin >> n;
	cin >> k;

	int mini = 99999;
	for (int i = 1; i <= n; i++)
	{
		for (int j = 1; j <= i; j++)
		{
			cin >> a;
			if (how_many_to_remove(n, i, j) <= k && a<mini)mini = a;
		}
	}
	cout << mini;

	return 0;
}