#include<bits/stdc++.h>
using namespace std;
#define PII pair<int,int>
#define st first
#define nd second
#define LL long long
#define pushb push_back
#define popb pop_back
#define cerr if(1) cout
#define sz(x) (int)x.size()
#define _upgrade ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0)
const int MXN=2e3, INF=1e9;
int n, k;
int tab[MXN+5][MXN+5], dp[MXN+5][MXN+5];
int safe( int i, int j )
{
if( i<0 || j<0 || j>i ) return 0;
return dp[i][j]+1;
}
void countt( )
{
for( int i=0; i<n; i++ )
for( int j=0; j<=i; j++ )
dp[i][j]=safe(i-1,j-1) + safe(i-1,j) - safe(i-2,j-1);
}
int main( )
{
_upgrade;
cin>>n>>k;
for( int i=0; i<n; i++ )
for( int j=0; j<=i; j++ )
cin>>tab[i][j];
countt();
int ans=INF;
for( int i=0; i<n; i++ ){
for( int j=0; j<=i; j++ )
if( dp[i][j]<k ) ans=min(tab[i][j],ans);
}
cout<<ans<<'\n';
}