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#include <bits/stdc++.h>
#define ll long long
#define mp make_pair
#define pb push_back
#define ld long double
#define ss(x) (int) x.size()
#define fi first
#define se second
#define cat(x) cout << #x << " = " << x << endl

using namespace std;

const int nax = 2010;

int n, k;
int a[nax][nax];
int dp[nax][nax];

int main() {
	scanf("%d %d", &n, &k);
	for(int i = 1; i <= n; ++i)
		for(int j = 1; j <= i; ++j)
			scanf("%d", &a[i][j]);
	int MAX = 3000;
	for(int i = 1; i <= n; ++i)
		for(int j = 1; j <= i; ++j) {
			if(j == 1 || i == j)
				dp[i][j] = i;
			else
				dp[i][j] = dp[i - 1][j - 1] + dp[i - 1][j] - dp[i - 2][j - 1] + 1;
			if(dp[i][j] <= k)
				MAX = min(MAX, a[i][j]);
		}
	printf("%d", MAX);
	
	
			
	
	return 0;
}