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#ifndef LOCAL
#pragma GCC optimize("O3")
#endif
#include <bits/stdc++.h>
using namespace std;
#define sim template < class c
#define ris return * this
#define mor > muu & operator << (
#define R22(r) sim > typename \
  enable_if<1 r sizeof dud<c>(0), muu&>::type operator<<(c g) {
sim > struct rge {c b, e; };
sim > rge<c> range(c h, c n) { return {h, n}; }
sim > auto dud(c * r) -> decltype(cerr << *r);
sim > char dud(...);
struct muu {
#ifdef LOCAL
stringstream a;
~muu() { cerr << a.str() << endl; }
R22(<) a << boolalpha << g; ris; }
R22(==) ris << range(begin(g), end(g)); }
sim, class b mor pair < b, c > r) { ris << "(" << r.first << ", " << r.second << ")"; }
sim mor rge<c> u) {
a << "[";
for (c i = u.b; i != u.e; ++i) 
  *this << ", " + 2 * (i == u.b) << *i;
 ris << "]";
 }
#else
sim mor const c&) { ris; }
#endif
muu & operator()() { ris; }
};
#define imie(r...) "[" #r ": " << (r) << "] "
#define debug (muu() << __FUNCTION__ << "#" << __LINE__ << ": ")

const int N = 2002;

int zdejm[N][N];
int rok[N][N];

const int inf = 1e9;

void solve() {
	int n, k;
	//~ if (!(
		cin >> n >> k;
		//~ )) {
		//~ exit(0);
	//~ }
	zdejm[1][1] = 1;
	for (int i = 2; i <= n; i ++) {
		for (int j = 1; j <= i; j ++) {
			zdejm[i][j] = zdejm[i-1][j-1] + zdejm[i-1][j] + 1;
			if (j == 1 || j == i) {
			} else {
				zdejm[i][j] -= zdejm[i-2][j-1];
			}
		}
	}
	int res = inf;
	for (int i = 1; i <= n; i ++) {
		for (int j = 1; j <= i; j ++) {
			cin >> rok[i][j];
			//~ cout << zdejm[i][j] << " ";
			if (zdejm[i][j] <= k) {
				res = min(res, rok[i][j]);
			}
		}
		//~ cout << "\n";
	}
	cout << res << "\n";
}

int main() {
	ios_base::sync_with_stdio(0);
	//~ while(true) {
		solve();
	//~ }
}