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#include <iostream>
#include <queue>

using namespace std;

#define MAX_LEVEL_SIZE 2010
#define INF 2030

int pyramid[MAX_LEVEL_SIZE][MAX_LEVEL_SIZE];

int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);

	int n, k, min_year = INF, a;

	cin >> n >> k;

	for (int i = 0; i < n; i++)
	{
		for (int j = 0; j <= i; j++)
		{
			cin >> a;
			
			if (j == 0 || j == i)
			{
				pyramid[i][j] = i + 1;
			}
			else
			{
				pyramid[i][j] = pyramid[i - 1][j - 1] + pyramid[i - 1][j] - pyramid[i - 2][j - 1] + 1;
			}

			if (pyramid[i][j] <= k)
			{
				min_year = min(min_year, a);
			}
		}
	}

	cout << min_year;
}