#include <iostream>
#include <vector>

using LL = long long;
int main() {
  std::ios_base::sync_with_stdio(false);
  
  int n,k,a;
  std::cin >> n >> k;
  
  std::vector<std::vector<int>> A(n);
  
  for (int i = 0; i < n; ++i) 
    for (int j = 0; j <= i; ++j) {
      std::cin >> a;
      A[j].push_back(a);
    }
    
  
  int Min = A[0][0];
  for (int j = 0; j < std::min(k, int(A.size())); ++j) {
    for (int i = 0; i < int(A[j].size()) && (1 + i)*(1 + j) <= k ; ++i) Min = std::min(Min, A[j][i]);
  }
  
  std::cout << Min << "\n";
  
  return 0;
}