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#include<bits/stdc++.h>
#include<chrono>
#define ff first
#define ss second
#define eb emplace_back
#define putchar putchar_unlocked
#define getchar getchar_unlocked
#define debug if(0)
using namespace std;
typedef long long int LL;
typedef long double LD;
typedef short int SH;

inline void readI(int *i)
{
	register int r=0;
	register char c=getchar();
	int z=1;
	if(c == '-')
	{
		z=-1;
	}
	while(c < '0' || c > '9')
	{
		c=getchar();
		if(c == '-')
		{
			z=-1;
		}
	}
	while(c >= '0' && c <= '9')
	{
		r=(r<<3)+(r<<1)+c-'0';
		c=getchar();
	}
	*i=(r*z);
}
inline void readUI(int *i)
{
	register int r=0;
	register char c=getchar();
	while(c < '0' || c > '9')
	{
		c=getchar();
	}
	while(c >= '0' && c <= '9')
	{
		r=(r<<3)+(r<<1)+c-'0';
		c=getchar();
	}
	*i=r;
}
inline void readLL(LL *l)
{
	register LL r=0;
	register char c=getchar();
	int z=1;
	if(c == '-')
	{
		z=-1;
	}
	while(c < '0' || c > '9')
	{
		c=getchar();
		if(c == '-')
		{
			z=-1;
		}
	}
	while(c >= '0' && c <= '9')
	{
		r=(r<<3)+(r<<1)+c-'0';
		c=getchar();
	}
	*l=(r*z);
}
inline void readULL(LL *l)
{
	register LL r=0;
	register char c=getchar();
	while(c < '0' || c > '9')
	{
		c=getchar();
	}
	while(c >= '0' && c <= '9')
	{
		r=(r<<3)+(r<<1)+c-'0';
		c=getchar();
	}
	*l=r;
}
inline void write(LL l)
{
	if(!l)
	{
		putchar(48);
	}
	else
	{
		if(l < 0)
		{
			l^=-1;
			++l;
			putchar(45);
		}
		int p=0,h[21];
		while(l)
		{
			++p;
			h[p]=(l%10)+48;
			l/=10;
		}
		for(int i=p+1; --i;)
		{
			putchar(h[i]);
		}
	}
}
inline void writeS(string s)
{
	int l=s.length();
	for(int i=0; i^l; ++i)
	{
		putchar(s[i]);
	}
}

int n,k,w=2020,tab[2007][2007],s[2007][2007];
int main()
{
	readUI(&n);
	readUI(&k);
	for(int i=1; n-i+1; ++i)
	{
		for(int j=1; i-j+1; ++j)
		{
			readUI(&tab[i][j]);
			s[i][j]=i-j+1+s[i-1][j-1];
		}
	}
	debug
	{
		for(int i=1; n-i+1; ++i)
		{
			for(int j=1; n-j+1; ++j)
			{
				printf("%d ", tab[i][j]);
			}
			putchar(10);
		}
		putchar(10);
		for(int i=1; n-i+1; ++i)
		{
			for(int j=1; n-j+1; ++j)
			{
				printf("%d ", s[i][j]);
			}
			putchar(10);
		}
		putchar(10);
	}
	for(int i=1; n-i+1; ++i)
	{
		for(int j=1; i-j+1; ++j)
		{
			if(s[i][j] <= k)
			{
				w=min(w, tab[i][j]);
			}
		}
	}
	write(w);
	return 0;
}
/*
5 7
1999
2019 2010
850 1500 1600
900 900 710 900
1000 800 600 800 1000
*/