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/*
 *  Copyright (C) 2019  Paweł Widera
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details:
 *  http://www.gnu.org/licenses/gpl.html
 */
#include <iostream>
using namespace std;

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);

	int n, k, year;
	int oldest = 2020;

	cin >> n >> k;

	for (int level = 1; level <= n; level++) {
		for (int i = 0; i < level; i++) {
			cin >> year;

			// if "bottle distance" is below the threshold
 			if ((i + 1) * (level - i) <= k) {
				oldest = min(oldest, year);
			}
		}
	}

	cout << oldest << endl;
	return 0;
}