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#include <bits/stdc++.h>
using namespace std;

vector<int> wine, cost;
int n, k;
int min_val, ind;

int main() {
	ios_base::sync_with_stdio(0);
	cin.tie(0);

	cin >> n >> k;
	
	wine.resize(n*(n+1)/2);
	cost.resize(n*(n+1)/2);
	
	for (int i = 0; i < n*(n+1)/2; i++)
		cin >> wine[i];

	min_val = 0;
	ind = 0;
	int max_iter = min(n, k);

	for (int h = 1; h <= max_iter; h++) {
		for (int i = 0; i < h; i++) {
			if (i == 0 || i == h - 1)
				cost[ind + i] = h;
			else
				cost[ind + i] = 1 + cost[ind - h + i] + cost[ind - h + i + 1] - cost[ind - 2*h + 2 + i];
			if (cost[ind + i] <= k && (min_val == 0 || wine[ind + i] < min_val))
				min_val = wine[ind + i];
		}
		ind += h;
	}
	
	cout << min_val << endl;
}