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#include <bits/stdc++.h> // Sylwia Szunejko
using namespace std;     // XIII LO Szczecin
using LL = long long;    // Poland
#define FOR(i, l, r) for(int i = (l); i <= (r); ++i)
#define REP(i, n) FOR(i, 0, (n) - 1)
template<class T> int size(T &&x) {
	return int(x.size());
}
template<class A, class B> ostream& operator<<(ostream &out, const pair<A, B> &p) {
	return out << '(' << p.first << ", " << p.second << ')';
}
template<class T> auto operator<<(ostream &out, T &&x) -> decltype(x.begin(), out) {
	out << '{';
	for(auto it = x.begin(); it != x.end(); ++it)
		out << *it << (it == prev(x.end()) ? "" : ", ");
	return out << '}';
}
void dump() {}
template<class T, class... Args> void dump(T &&x, Args... args) {
	cerr << x << ";  ";
	dump(args...);
}
#ifdef DEBUG
  struct Nl{~Nl(){cerr << '\n';}};
# define debug(x...) cerr << (strcmp(#x, "") ? #x ":  " : ""), dump(x), Nl(), cerr << ""
#else
# define debug(...) 0 && cerr
#endif
mt19937_64 rng(0);
int rd(int l, int r) {
	return uniform_int_distribution<int>(l, r)(rng);
}
// end of templates

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

	int n, k;
	cin >> n >> k;
	vector<vector<int>> pir(n), dp(n);
	FOR(i, 1, n)
	{
		debug(i);
		pir[i - 1].resize(i);
		dp[i - 1].resize(i);
		REP(j, i)
			cin >> pir[i - 1][j];
	}
	int wyn = int(1e9);
	dp[0][0] = 1;
	wyn = min(wyn, pir[0][0]);
	debug(dp);
	FOR(i, 1, n - 1)
	{
		REP(j, i + 1)
		{
			if(j - 1 < 0)
				dp[i][j] = dp[i - 1][j] + 1;
			else if(j > i - 1)
				dp[i][j] = dp[i - 1][j - 1] + 1;
			else
				dp[i][j] = dp[i - 1][j - 1] + dp[i - 1][j] - dp[i - 2][j - 1] + 1;
			debug(dp[i][j]);
			if(dp[i][j] <= k)
				wyn = min(wyn, pir[i][j]);
		}
	}
	debug(dp);
	cout << wyn;

}