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#include<bits/stdc++.h>
#define MAGICLINE ios_base::sync_with_stdio(0)
#define FOR(i, a, b) for(auto (i)=(a);(i)<=(b);(i)++)
#define DFOR(i, a, b) for(auto (i)=(a);(i)>=(b);(i)--)
#define REP(i, a) for(auto (i)=0;(i)<(a);(i)++)
#define ALL(V) (V).begin(), (V).end()
#define translate(V) sort(ALL(V)); (V).resize(unique(ALL(V))-(V).begin())
#define roll(a, b) ((a)+rand()%((b)-(a)+1))
#define pb push_back
#define mp make_pair
#define se second
#define fs first
#define even(a) (!((a) & 1))
using namespace std;
typedef long long LL;
typedef long double LD;
typedef pair<int, int> PII;
typedef pair<LL, int> PLI;
typedef priority_queue<int> PQI;
typedef priority_queue<LL> PQL;

const int MN = 2003, INF = 1e9+7;
int inp[MN][MN], T[MN][MN];

int f(int x){
  return x*(x+1)/2;
}

int main(){
  MAGICLINE;
  int n, k; scanf("%d %d", &n, &k);
  int ans = INF;

  FOR(i, 1, n){
    FOR(j, 1, i){
      scanf("%d", &inp[i][j]);
      T[i][j] = min(T[i-1][j-1]+i-j, T[i-1][j]+j-1)+1;
      if(k >= T[i][j]) ans = min(ans, inp[i][j]);
    }
  }

  printf("%d\n", ans);
  return 0;
}