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#include <iostream>
#include <vector>

void checkLess(int key, int val, std::vector<int>& minYears)
{
  if((minYears[key] == 2020) || (minYears[key] > val))
  {
    minYears[key] = val;
  }
}

int main()
{
  int n, k;
  std::cin>>n>>k;
  std::vector<int> minYears(n * n, 2020);
  std::vector<int> diffs;
  diffs.push_back(1);
  std::cin>>minYears[1];
  if(n == 1)
  {
    std::cout<<minYears[1]<<"\n";
    return 0;
  }
  std::cin>>minYears[2];
  int val;
  std::cin>>val;
  if(val < minYears[2])
  {
    minYears[2] = val;
  }
  int last = n;
  for(int r = 3; r <= last; ++r)
  {
    if(r % 2 == 1)
    {
      diffs.push_back(1);
    }
    std::vector<int> v(r + 1, 0);
    int mid = (r / 2) + (r % 2);
    for(int c = 1; c <= mid; ++c)
    {
      if(c == 1)
      {
        v[c] = r;
      }
      else
      {
        v[c] = v[c - 1] + diffs[c - 1];
        ++ diffs[c - 1];
      }
      std::cin>>val;
      checkLess(v[c], val, minYears);
    }
    int a = mid;
    int b = mid;
    if(r % 2 == 0)
    {
      ++b;
    }
    for(int c = 1; c <= r / 2; ++c)
    {
      v[a + c] = v[b - c];
      std::cin>>val;
      checkLess(v[a + c], val, minYears);
    }
  }
  int res = 2020;
  for(int i = 1; i <= k; ++i)
  {
    if(minYears[i] < res)
    {
      res = minYears[i];
    }
  }
  std::cout<<res<<"\n";
}