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#include <bits/stdc++.h>

using namespace std;

int main() {
#ifdef LOCAL
  freopen("input.txt", "r", stdin);
#endif
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, k;
  cin >> n >> k;
  int ans = 2019;
  for (int i = 2; i <= n + 1; ++i) {
    for (int j = 1; j < i; ++j) {
      int x;
      cin >> x;
      if (j * (i - j) <= k) {
        ans = min(ans, x);
      }
    }
  }
  cout << ans << "\n";
  return 0;
}