#pragma GCC optimize("O3")
#include <bits/stdc++.h>
#define ll long long
#define str string
#define pb push_back
#define pf push_front
#define in insert
#define all(v) v.begin(),v.end()
#define fastIO ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
const int sz=61,INF=1000000000;
using namespace std;
ll n,m,ans=-INF;
vector<vector<ll>>nums(sz,vector<ll>(sz));
vector<vector<bool>>isSeen(sz,vector<bool>(sz));
void dfs(ll num1,ll num2,ll num3,ll num4,ll num5)
{
if(num1>=1 && num1<=n && num2>=1 && num2<=m && !isSeen[num1][num2])
{
isSeen[num1][num2]=true;
ans=max(ans,num4-num3-num5);
dfs(num1+1,num2,min(num3,nums[num1+1][num2]),max(num4,nums[num1+1][num2]),num5+1);
dfs(num1-1,num2,min(num3,nums[num1-1][num2]),max(num4,nums[num1-1][num2]),num5+1);
dfs(num1,num2+1,min(num3,nums[num1][num2+1]),max(num4,nums[num1][num2+1]),num5+1);
dfs(num1,num2-1,min(num3,nums[num1][num2-1]),max(num4,nums[num1][num2-1]),num5+1);
}
}
void solve()
{
cin>>n>>m;
for(int i=1;i<=n;i++)
{
for(int j=1;j<=m;j++)
{
cin>>nums[i][j];
}
}
for(int i=1;i<=n;i++)
{
for(int j=1;j<=m;j++)
{
for(int k=0;k<sz;k++)
{
for(int l=0;l<sz;l++)
{
isSeen[k][l]=false;
}
}
dfs(i,j,nums[i][j],nums[i][j],1);
}
}
cout<<ans;
}
int main()
{
fastIO;
ll t=1;
//cin>>t;
while(t--)
{
solve();
}
}
