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#include <bits/stdc++.h>
#ifdef LOC
#include "debuglib.h"
#else
#define deb(...)
#define DBP(...)
#endif
using namespace std;
using   ll         = long long;
using   Vi         = vector<int>;
using   Pii        = pair<int, int>;
#define pb           push_back
#define mp           make_pair
#define x            first
#define y            second
#define rep(i, b, e) for (int i = (b); i < (e); i++)
#define each(a, x)   for (auto& a : (x))
#define all(x)       (x).begin(), (x).end()
#define sz(x)        int((x).size())

int main() {
	cin.sync_with_stdio(0); cin.tie(0);
	cout << fixed << setprecision(18);

	int n, k; cin >> n >> k;
	int best = INT_MAX;

	rep(lvl, 1, n+1) {
		rep(i, 0, lvl) {
			int e; cin >> e;
			if ((i+1)*(lvl-i) <= k) {
				best = min(best, e);
			}
		}
	}

	cout << best << endl;
	return 0;
}