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#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;

const int ene = 2002;
int t[ene][ene];
vector< pair<int,int> > v;

int main()
{
  int n,k;
  cin >> n >> k;
  t[1][1] = 1;
  for(int i = 1; i <= n; i++)
  {
    for(int j = 1; j <= i; j++)
    {
      int a;
      cin >> a;
      t[i][j] = t[i-1][j]+j;
      //cout << t[i][j] << "\n";
      v.push_back({a,t[i][j]});
    }
  }
  sort(v.begin(), v.end());
  for(int i = 0; i < v.size(); i++)
  {
    if(v[i].second <= k)
    {
      cout << v[i].first << "\n";
      return 0;
    }
  }
  return 0;
}