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#include <bits/stdc++.h>
#include <unordered_set>
using namespace std;
 
#define st first
#define nd second
#define pb push_back
#define mp make_pair
#define klar(v) memset(v, 0, sizeof(v))
#define bust ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
#define gcd(a, b) __gcd(a, b);
#define debug(x) cout << #x << " " << x << endl;
#define endl "\n"
 
typedef vector<int> vi;
typedef vector<pair<int, int> > vpii;
typedef vector<long long> vll;
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;
typedef long long ll;
const int maxn = 2e3+100;

int h[maxn][maxn];
ll dp[maxn][maxn];

int main(){
    int n, k;
    cin >> n >> k;
    for(int i = 1; i <= n; i++){
        for(int j = 1; j <= i; j++){
          cin >>  h[i][j];  
        }
    }
	dp[1][1] = 1;
	for(int i = 2; i <= n; i++){
		for(int j = 1; j <= i; j++){
			dp[i][j] = dp[i-1][j] + dp[i-1][j-1] - dp[i-2][j-1] + 1;
		}
	}
	int ans = h[1][1];
	for(int i = 1; i <= n; i++){
		for(int j = 1; j <= i; j++){
			if(dp[i][j] <= k)
				ans = min(ans, h[i][j]);
		}
	}
	cout << ans << endl;
}