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#include <bits/stdc++.h>

using namespace std;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef long long LL;
typedef pair<int,int> PI; 
typedef pair<LL,LL> PLL;
typedef unsigned long long ULL;
typedef pair<double,double> PD;

#define FOR(x, b, e) for(int x = b; x<= (e); x++)
#define FORD(x, b, e) for(int x = b; x>= (e); x--)
#define REP(x, n) for(int x = 0; x<(n); ++x)
#define ALL(c) (c).begin(), (c).end()
#define SIZE(x) ((int)(x).size())

#define PB push_back
#define IN insert
#define ST first
#define ND second
#define INF 2000000011
#define MOD 1000000007

#define MAXS

int n,k;

int main(){

//	ios::sync_with_stdio(0); cin.tie(0);
	cin>>n>>k;
	
	vector<VI> dp(n+1,VI(n+1));
	
	int wyn=INF;
	int p=1;
	FOR(i,1,n){
		FOR(j,1,p){
			int a;
			cin>>a;
			if(i==1)
				dp[1][1]=1;
			else
				dp[i][j]=dp[i-1][j]+dp[i-1][j-1]-dp[i-2][j-1]+1;
			if(dp[i][j]<=k)
				wyn=min(wyn,a);
		}
		p++;
		if(p>n)
			break;
	}
	cout<<wyn;
	return 0;
}
/*
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*/