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#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll X_MAX = 2000*2000 + 5;

ll n;
ll k;
ll A [ X_MAX ] [ 2 ];
ll t [ X_MAX ];
ll toUnblock [ X_MAX ];
ll nrVertex;
ll numberOfElements;

void showNeighbours() {
	for ( ll i = 1; i <= numberOfElements; i++ ) {
		cout << i << ": ";
		if ( A [ i ] [ 0 ] == 0 ) {
			cout << "brak" << '\n';
		}
		else {
			cout << A [ i ] [ 0 ] << ' ' << A [ i ] [ 1 ]  << '\n';
		}
	}
}

void showToUnblock() {
	ll x = 0;
	for ( ll i = 1; i <= n; i++ ) {
		for ( ll j = 1; j <= i; j++ ) {
			x++;
			cout << toUnblock [ x ] << " ";
		}
		cout << '\n';
	}
	cout << '\n';
	cout << '\n';
}

void showt() {
	ll x = 0;
	for ( ll i = 1; i <= n; i++ ) {
		for ( ll j = 1; j <= i; j++ ) {
			x++;
			cout << t [ x ] << " ";
		}
		cout << '\n';
	}
	cout << '\n';
	cout << '\n';
}

int main() {
	ios_base::sync_with_stdio(0);

	cin >> n >> k;
	numberOfElements = (n*(n+1))/2;


	//utworzenie grafu
	for ( ll i = 1; i <= n; i++ ) {
		for ( ll j = 1; j <= i; j++ ) {
			nrVertex++;
			cin >> t [ nrVertex ];
			if ( i != n ) {
				A [ nrVertex ] [ 0 ] = nrVertex + i;
				A [ nrVertex ] [ 1 ] = nrVertex + i + 1;
			}
		}
	}

	
	ll i = 1;
	ll a = 1;
	ll b = -1;
	ll j = -1;

	toUnblock [ 1 ] = -1;
	while ( true ) {

		b = a + 1;
		j = i;
		toUnblock [ i ] = toUnblock [ i - a + 1 ] + 1;
		if ( i == 1 ) {
			toUnblock [ i ] = 0;
		}
		/*cout << "a: " << a << '\n';
		cout << "i: " << i << " " << "poprzedni: " << i - a + 1 << '\n';
		cout << i << ": " << toUnblock [ i ] << '\n';
		cout << '\n';*/
		while ( true ) {

			if ( i != j ) {
				toUnblock [ j ] = toUnblock [ j - b + 1 ] + a;
			}



			//ide dalej w prawo
			j += b;
			b++;
			if ( j > numberOfElements ) {
				break;
			}
		}



		//ide dalej w lewo
		i += a;
		a++;
		if ( i > numberOfElements) {
			break;
		}
	}

	ll res = 3000;
	for ( ll i = 1; i <= numberOfElements; i++ ) {
		if ( toUnblock [ i ] <= k ) {
			res = min(t [ i ], res );
		}
	}

	cout << res << '\n';


	//showt();
	//showToUnblock();

	return 0;
}
/*
						1
			2							3
		4				5						6
	7			8					9				10	
 11		12				13					14			15




*/