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#include <iostream>
#include <cstdio>
#include <vector>

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

	int n, k, c, res = 2020;
	scanf("%d %d", &n, &k);

	std::vector<int> lel1, lel2;

	for (int i = 1; i <= n; i++) {
		for (int j = 1; j < i; j++) {
			int t = lel1[j - 1] + j;
			scanf("%d", &c);
			if (t <= k && res > c) {
				res = c;
			}
			lel2.push_back(t);
		}
		scanf("%d", &c);
		if (i <= k && res > c) {
			res = c;
		}
		lel2.push_back(i);
		lel1.clear();
		for (int j = 0; j < lel2.size(); j++) lel1.push_back(lel2[j]);
		lel2.clear();
	}

	printf("%d\n", res);
}