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#include "bits/stdc++.h"

using namespace std;
#define PB push_back
#define LL long long
#define FOR(i,a,b) for (int i = (a); i <= (b); i++)
#define FORD(i,a,b) for (int i = (a); i >= (b); i--)
#define REP(i,n) FOR(i,0,(int)(n)-1)
#define st first
#define nd second
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((int)(x).size())
#define VI vector<int>
#define PII pair<int,int>
#define LD long double

template<class C> void mini(C& a4, C b4) { a4 = min(a4, b4); }
template<class C> void maxi(C& a4, C b4) { a4 = max(a4, b4); }

template<class TH> void _dbg(const char *sdbg, TH h){cerr<<sdbg<<"="<<h<<"\n";}
template<class TH, class... TA> void _dbg(const char *sdbg, TH h, TA... a) {
  while(*sdbg!=',')cerr<<*sdbg++;
  cerr<<"="<<h<<",";
  _dbg(sdbg+1, a...);
}

template<class T> ostream &operator<<(ostream &os, vector<T> V){
  os<<"[";for(auto vv:V)os<<vv<<",";return os<<"]";
} 

template<class L, class R> ostream &operator<<(ostream &os, pair<L,R> P) {
  return os << "(" << P.st << "," << P.nd << ")";
}


#ifdef LOCAL
#define debug(...) _dbg(#__VA_ARGS__, __VA_ARGS__)
#else
#define debug(...) (__VA_ARGS__)
#define cerr if(0)cout
#endif

struct Solution{
  int n,k;
  vector<VI> wiersze;
  vector<VI> dyn;
  int ans;
  Solution(int n_, int k_):
  n(n_), k(k_), wiersze(n), dyn(n){
    ans = INT_MAX;
    REP(i, n){
      wiersze[i].resize(i + 1);
      dyn[i].resize(i + 1);
      REP(j, i + 1){
        cin>>wiersze[i][j];
        dyn[i][j] = 1 + get_dyn(i - 1, j) +
          get_dyn(i - 1, j - 1) -
          get_dyn(i - 2, j - 1);
        if(dyn[i][j] <= k){
          ans = min(ans, wiersze[i][j]);
        }
      }
    }
  }
  int get_dyn(int i, int j){
    if(i < 0 || j < 0)
      return 0;
    if(SZ(dyn[i]) <= j){
      return 0;
    }
    return dyn[i][j];
  }
};

int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n,k;
  while(cin>>n>>k)
    cout<<Solution(n, k).ans<<"\n";
}