//UNSTOPPABLE
#include "bits/stdc++.h"
#include <ext/pb_ds/assoc_container.hpp>
#define ll long long
#define pb push_back
#define pf push_front
#define ppb pop_back
#define ppf pop_front
#define int long long
#define F first
#define S second
#define all(x) (x).begin(), (x).end()
#define pii pair<int,int>
#define tpii pair <pair <int,int> , int>
#define bruh cout << "NO\n"
using namespace std;
using namespace __gnu_pbds;
const int N = 107 , M = 5001;
int mod = 1e9 + 7;
const int INF = 1e9;
int n,m,a[N][N],num[N][N],val[M],used[M],mx[M][M],mn[M][M];
vector <int> g[M];
int dist[M][M];
void Goldik(){
cin >> n >> m;
int cur = 0;
for(int i = 1 ; i <= n ; i++){
for(int j = 1 ; j <= m ; j++){
cin >> a[i][j];
num[i][j] = ++cur;
val[cur] = a[i][j];
}
}
for(int i = 1 ; i <= n ; i++){
for(int j = 1 ; j <= m ; j++){
int x = num[i][j];
if(i != 1){
g[x].pb(num[i - 1][j]);
}
if(j != 1){
g[x].pb(num[i][j - 1]);
}
if(i != n){
g[x].pb(num[i + 1][j]);
}
if(j != m){
g[x].pb(num[i][j + 1]);
}
}
}
for(int i = 1 ; i <= cur ; i++){
for(int j = 1 ; j <= cur ; j++){
dist[i][j] = INF;
mx[i][j] = -INF;
mn[i][j] = INF;
}
}
int ans = -INF;
for(int i = 1 ; i <= cur ; i++){
for(int j = 1 ; j <= cur ; j++) used[j] = 0;
deque <int> q = {};
q.pb(i);
dist[i][i] = 1;
used[i] = 1;
mx[i][i] = val[i];
mn[i][i] = val[i];
while(q.size()){
int v = q.front();
q.ppf();
used[v] = 1;
for(auto to : g[v]){
if(!used[to]){
if(dist[i][to] == INF || dist[i][to] > dist[i][v] + 1){
dist[i][to] = dist[i][v] + 1;
mx[i][to] = max(mx[i][v] , val[to]);
mn[i][to] = min(mn[i][v] , val[to]);
q.pb(to);
}
}
}
}
for(int j = 1 ; j <= cur ; j++){
ans = max(ans , mx[i][j] - mn[i][j] - dist[i][j]);
}
}
cout << ans;
}
//5e7 -> max
//rewai mnogo zadach vozmozhno odna iz nih gde to popadetsya
//returning winter prime?
//chem prowe tem luchshe
signed main(/*AZ AZDAN UZDIKSIZ*/){
//freopen("txt.in","r",stdin);
//freopen("txt.out","w",stdout);
ios_base::sync_with_stdio(0);
cin.tie(0);
srand(time(0));
int TT = 1;
// cin >> TT;
for(int i = 1 ; i <= TT ; i++){
//cout << "Case " << i << ": ";
Goldik();
}
}
