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#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
using ll	= long long;
using ull	= unsigned long long;
using ld	= long double;
using pii	= pair<int,int>;
using pll	= pair<ll,ll>;
using vi	= vector<int>;
using vb	= vector<bool>;
using vc	= vector<char>;
using vvc	= vector<vc>;
using vvi	= vector<vi>;
using vvb	= vector<vb>;
using vpii	= vector<pii>;
using vpll	= vector<pll>;
using vll	= vector<ll>;
using vvll	= vector<vll>;
using vull	= vector<ull>;
#define f first
#define s second
#define pb emplace_back
#define sz size()
#define graph vector<vertex>
#define rep(i, begin, end) for(__typeof(end) i = (begin); i <= (end); ++i)
#define repr(i, begin, end) for(__typeof(end) i = (begin); i >= (end); --i)
#define bend(X) X.begin(), X.end()
#define print cout<<
#ifdef LOCAL
#define nl << endl
#define deb(x) cout << #x << " = " << x << endl
#define say(x) cout << x << endl
#else
#define nl << '\n'
#define deb(x)
#define say(x)
#endif
constexpr int INF = 2000000000;
constexpr ll INFl = 2000000000ll;
constexpr ll INFll = 2000000000000000000ll;
constexpr ll mod = 1e9+7;
struct num {
	num(ll val = 0) : v{val} {if(v>=mod) v %= mod;};
	ll v;
	operator ll() {return v;};
	num operator+(const num& o) const {return {v+o.v};};
	num operator-(const num& o) const {return {v-o.v+mod};};
	num operator*(const num& o) const {return {v*o.v};};
	num operator+=(const num& o) {v = num{v+o.v}; return *this;};
	num operator-=(const num& o) {v = num{v-o.v+mod}; return *this;};
	num operator*=(const num& o) {v = num{v*o.v}; return *this;};
	num operator!() const { num R = 1; rep(i, 2, v+1) R *= num{i}; return R; }
	num operator^(ll b) const {
		num R{1}, a{v};	while(b > 0) { if(b&1) R *= a; a *= a, b /= 2; } return R;
	}
	num operator/(const num& o) const { return (*this)*(o^(mod-2)); }
};
template <typename T1, typename T2> ostream& operator<<(ostream& os, pair<T1,T2> x) {
	os << '(' << x.f << ' ' << x.s << ')'; return os;
}
template <typename T1, typename T2> istream& operator>>(istream& is, pair<T1,T2>& x) {
	is >> x.f >> x.s; return is;
}
template <typename T> ostream& operator<<(ostream& os, vector<T>& x) {
	for(T& i : x) os << i << ' '; return os;
}
template <typename T> istream& operator>>(istream& is, vector<T>& x) {
	for(T& i : x) is >> i; return is;
}
template <typename T1, typename T2>
pair<T1,T2> operator+(const pair<T1,T2>& A, const pair<T1,T2>& B) { return {A.f+B.f, A.s+B.s}; }
template <typename T1, typename T2>
pair<T1,T2> operator-(const pair<T1,T2>& A, const pair<T1,T2>& B) { return {A.f-B.f, A.s-B.s}; }
template <typename T1, typename T2>
pair<T1,T2> operator-(const pair<T1,T2>& A) { return {-A.f, -A.s}; }
template<typename T1, typename T2> bool maxe(T1& A, const T2& B) {if(B>A){A=B;return 1;}return 0;}
template<typename T1, typename T2> bool mine(T1& A, const T2& B) {if(B<A){A=B;return 1;}return 0;}

//
// END OF DEFINES
//

int n, k;
vvi T;

bool in() {
	cin >> n >> k;
	T.resize(n+1, vi(n+1));
	rep(i, 1, n)
		rep(j, 1, i)
			cin >> T[i][j];
	
	return true;
}

inline ll cost(int i, int j) {
	return ll(j)*ll(i-j+1);
}

ll solve() {
	ll R = INF;
	rep(i, 1, n)
		rep(j, 1, i)
			if(cost(i, j) <= k)
				mine(R, T[i][j]);
	return R;
	
	return -INF;
}



int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	int noOfTests = 1;
	//cin >> noOfTests;
	
	while(noOfTests --> 0) {
		if(!in()) {
			cout << "popsute_wejscie\n";
			continue;
		}
		ll result = solve();
		if(result == ll(-'t'))
			cout << "TAK\n";
		else if(result == ll(-'n'))
			cout << "NIE\n";
		else if(result == ll(-'e'))
			cout << "Popsute\n";
		else if(result != -INF)
			cout << result << '\n';
	}
	
	return 0;
}