#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define N 600005
#define pb push_back
#define ff first
#define ss second
#define all(x) x.begin(),x.end()
#define sz(s) (int)s.size()
#define pii pair<int,int>
//mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
ll T, n, a[2000][2000], t, m, answer, vis[2000][2000];
void solve(int x,int y,int cur1,int cur2,ll mn,ll mx,int cnt) {
if(x <= 0 || y <= 0 || x > n || y > m || vis[x][y] == 1) return;
vis[x][y] = 1;
answer = max(answer,mx - mn - cnt);
solve(x + 1, y , cur1,cur2,min(mn,a[x + 1][y]),max(mx,a[x+1][y]),cnt+1);
solve(x-1, y , cur1,cur2,min(mn,a[x-1][y]),max(mx,a[x-1][y]),cnt+1);
solve(x, y + 1, cur1,cur2,min(mn,a[x][y + 1]),max(mx,a[x][y + 1]),cnt+1);
solve(x, y - 1, cur1,cur2,min(mn,a[x][y - 1]),max(mx,a[x][y - 1]),cnt+1);
vis[x][y] = 0;
}
int main () {
ios::sync_with_stdio(0);cin.tie(0);
cin >> n >> m;
for(int i = 1;i <= n;i++) {
for(int j = 1;j <=m;j++) {
cin >> a[i][j];
}
}
for(int i=1;i<=n;i++){
for(int j= 1;j<=m;j++) {
solve(i,j,i,j,a[i][j],a[i][j],1);
}
}
cout << answer << '\n';
}
