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#include <bits/stdc++.h>
using namespace std;

typedef unsigned long long ull;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> PII;
typedef pair<ll, int> PILL;
typedef pair<ll, ll> PLL;

const int MAX_N = 1e5+5;
const int M = 1e6;
const ll INF = (ll)(1e18);
const int inf = 1e9;
const ll MOD = 1000000007LL;

int n, k;
int a[2005][2005];
int dp[2005][2005];

void solve() {
    cin >> n >> k;
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= i; j++) {
            cin >> a[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-1] + dp[i-1][j] - dp[i-2][j-1] + 1;
        }
    }

    int ans = inf;
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= i; j++) {
            if (dp[i][j] <= k) {
                ans = min(ans, a[i][j]);
            }
        }
    }


    cout << ans;

}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);

    solve();


    return 0;
}