#include "bits/stdc++.h"
using namespace std;
#define FAST ios_base::sync_with_stdio(false); cin.tie(0);
#define pb push_back
#define eb emplace_back
#define ins insert
#define ph push
#define f first
#define s second
#define cbr cerr << "hi\n"
#define mmst(x, v) memset((x), v, sizeof ((x)))
#define siz(x) ll(x.size())
#define all(x) (x).begin(), (x).end()
#define lbd(x, y) lower_bound(all(x), y)
#define ubd(x, y) upper_bound(all(x), y)
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count()); //can be used by calling rng() or shuffle(A, A+n, rng)
inline long long rand(long long x, long long y) { return (rng() % (y+1-x)) + x; } //inclusivesss
string inline to_string(char c) {string s(1,c);return s;} template<typename T> inline T gcd(T a,T b){ return a==0?llabs(b):gcd(b%a,a); }
typedef int ll;
typedef long double ld;
#define FOR(i,s,e) for(ll i=s;i<=ll(e);++i)
#define DEC(i,s,e) for(ll i=s;i>=ll(e);--i)
typedef pair<ll,ll>pi; typedef pair<ll,pi>spi; typedef pair<pi,pi>dpi;
#define LLINF INF //((long long)1e18)
#define INF int(1e9+1e6)
#define MAXN (1006)
int n,m,dist[MAXN][MAXN],grid[MAXN][MAXN],ans=-LLINF;
#define gc getchar_unlocked
void in(int &x){
x=0;
char ch=gc();
while(ch<'0'||ch>'9')ch=gc();
while(ch>='0'&&ch<='9'){
x=(x<<3)+(x<<1)+ch-48;
ch=gc();
}
}
vector<spi> v;
int main(){
// FAST
in(n),in(m);
FOR(i,1,n)FOR(j,1,m)in(grid[i][j]);
queue<pi> pq;
FOR(i,1,n)FOR(j,1,m)v.eb(grid[i][j]-1,pi(i,j));
sort(all(v));
ll dx[]={0,0,1,-1};
ll dy[]={1,-1,0,0};
mmst(dist,-1);
while(pq.size()||v.size()){
ll x,y,d;
if(v.empty() || (pq.size() && dist[pq.front().f][pq.front().s] >= v.back().f)) x=pq.front().f,y=pq.front().s,d=dist[x][y],pq.pop();
else x=v.back().s.f,y=v.back().s.s,d=v.back().f,dist[x][y]=v.back().f,v.pop_back();
if(dist[x][y]^d)continue;
ans=max(ans,d-grid[x][y]);
FOR(i,0,3){
ll nx=x+dx[i];
ll ny=y+dy[i];
if(nx<=0||nx>n||ny<=0||ny>m)continue;
if(dist[nx][ny]==-1){
dist[nx][ny]=d-1;
if(dist[nx][ny]<ans)continue;
pq.emplace(pi(nx,ny));
}else assert(dist[nx][ny]>=d-1);
}
}
cout<<ans<<'\n';
}
