#include <bits/stdc++.h>
using namespace std;
#if __has_include(<atcoder/all>)
#include <atcoder/all>
using namespace atcoder;
template<int mod>istream &operator>>(istream &is,static_modint<mod> &a){long long b;is>>b;a=b;return is;}
istream &operator>>(istream &is,modint &a){long long b;cin>>b;a=b;return is;}
#endif
#ifdef LOCAL
#include "debug.h"
#else
#define debug(...) static_cast<void>(0)
#define debugg(...) static_cast<void>(0)
template<typename T1,typename T2>ostream &operator<<(ostream &os,const pair<T1,T2>&p){os<<p.first<<' '<<p.second;return os;}
#endif
using ll=long long;
using ull=unsigned long long;
using P=pair<ll,ll>;
template<typename T>using minque=priority_queue<T,vector<T>,greater<T>>;
template<typename T>bool chmax(T &a,const T &b){return (a<b?(a=b,true):false);}
template<typename T>bool chmin(T &a,const T &b){return (a>b?(a=b,true):false);}
template<typename T1,typename T2>istream &operator>>(istream &is,pair<T1,T2>&p){is>>p.first>>p.second;return is;}
template<typename T>istream &operator>>(istream &is,vector<T> &a){for(auto &i:a)is>>i;return is;}
template<typename T1,typename T2>void operator++(pair<T1,T2>&a,int n){a.first++,a.second++;}
template<typename T1,typename T2>void operator--(pair<T1,T2>&a,int n){a.first--,a.second--;}
template<typename T>void operator++(vector<T>&a,int n){for(auto &i:a)i++;}
template<typename T>void operator--(vector<T>&a,int n){for(auto &i:a)i--;}
#define reps(i,a,n) for(int i=(a);i<(n);i++)
#define rep(i,n) reps(i,0,n)
#define all(x) x.begin(),x.end()
#define pcnt(x) __builtin_popcountll(x)
ll myceil(ll a,ll b){return (a+b-1)/b;}
template<typename T,size_t n,size_t id=0>
auto vec(const int (&d)[n],const T &init=T()){
  if constexpr (id<n)return vector(d[id],vec<T,n,id+1>(d,init));
  else return init;
}
void SOLVE();
int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  #ifdef LOCAL
  clock_t start=clock();
  #endif
  int testcase=1;
  //cin>>testcase;
  for(int i=0;i<testcase;i++){
    SOLVE();
  }
  #ifdef LOCAL
  cerr<<"time:";
  cerr<<(clock()-start)/1000;
  cerr<<"ms\n";
  #endif
}
int h,w;
inline bool inarea(int x,int y){
  return 0<=x&&0<=y&&x<h&&y<w;
}
vector<pair<int,int>>around(int x,int y){
  vector<pair<int,int>>ret;
  vector<int>dx{1,0,-1,0},dy{0,1,0,-1};
  rep(i,4){
    int cx=x+dx[i],cy=y+dy[i];
    if(inarea(cx,cy))ret.emplace_back(cx,cy);
  }
  return ret;
}
vector<pair<int,int>>around8(int x,int y){
  vector<pair<int,int>>ret;
  vector<int>dx{1,1,0,-1,-1,-1,0,1},dy{0,1,1,1,0,-1,-1,-1};
  rep(i,8){
    int cx=x+dx[i],cy=y+dy[i];
    if(inarea(cx,cy))ret.emplace_back(cx,cy);
  }
  return ret;
}
void SOLVE(){
  cin>>h>>w;
  vector<vector<int>>a(h,vector<int>(w));
  cin>>a;
  vector<vector<int>>to(h*w),pre(h*w);
  vector<int>cnt(h*w,0);
  rep(i,h)rep(j,w){
    for(auto [x,y]:around(i,j))if(a[i][j]<a[x][y]){
      to[i*w+j].push_back(x*w+y);
      pre[x*w+y].push_back(i*w+j);
      cnt[x*w+y]++;
    }
  }
  queue<int>que;
  rep(i,h*w)if(cnt[i]==0)que.push(i);
  debug(to,pre,cnt);
  vector<int>dp(h*w,0);
  while(!que.empty()){
    int u=que.front();
    que.pop();
    for(auto i:pre[u])chmax(dp[u],dp[i]+1);
    for(auto i:to[u])if(!--cnt[i])que.push(i);
  }
  debug(cnt);
  cout<<*max_element(all(dp))+1<<endl;
}