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#include <bits/stdc++.h>
#define lld long long
#define pii pair<int,int>
#define mp make_pair
#define s second
#define f first
#define pb push_back
#ifdef WIN32
#define gcx getchar()
#elif __linux__
#define gcx getchar_unlocked()
#endif

using namespace std;

void scam(int *x)
{
	int tt = 0;
	char z = '@';
	while(z<'0' || z>'9')z=gcx;
	while((z>='0') && (z<='9')) tt = (tt<<3) + (tt<<1) + z - '0', z=gcx;
	*x = tt;
}

int dp[2048][2048];
int n,k,mn=1000000000;
int t[2048][2048];

int main()
{
	scam(&n); scam(&k);

	for(int i=0;i<n;++i){
		for(int j=0;j<=i;++j){
			scam(&t[i][j]);
		}
	}
	dp[0][0]=1;
	dp[1][0]=2;
	dp[1][1]=2;
	for(int i=2;i<n;++i)
	{
		dp[i][0]=i+1;
		for(int j=1;j<=i;++j){
			dp[i][j]=1+dp[i-1][j-1]+dp[i-1][j]-dp[i-2][j-1];
		}
	}
	for(int i=0;i<n;++i){
		for(int j=0;j<=i;++j){
			//printf("%d ",dp[i][j]);
			if(dp[i][j]<=k) mn=min(mn,t[i][j]);
		}
		//puts("");
	}
	printf("%d",mn);
	
	return 0;
}