#include <iostream>
using namespace std;
#define int long long
int v[1001][1001];
int aux[1001][1001][4];
signed main()
{
ios_base::sync_with_stdio(false);cin.tie(NULL);
int n,m,rasp=0,i,j,j1;
cin>>n>>m;
for(i=1;i<=n;i++){
for(j=1;j<=m;j++){
cin>>v[i][j];
}
}
for(i=1;i<=n;i++){
for(j=1;j<=m;j++)
aux[i][j][0]=max(max(aux[i][j-1][0],aux[i-1][j][0]),v[i][j])-1;
for(j=m;j>=1;j--)
aux[i][j][1]=max(max(aux[i][j+1][1],aux[i-1][j][1]),v[i][j])-1;
}
for(i=n;i>=1;i--){
for(j=1;j<=m;j++)
aux[i][j][2]=max(max(aux[i][j-1][2],aux[i+1][j][2]),v[i][j])-1;
for(j=m;j>=1;j--)
aux[i][j][3]=max(max(aux[i][j+1][3],aux[i+1][j][3]),v[i][j])-1;
}
for(i=1;i<=n;i++){
for(j=1;j<=m;j++){
for(j1=0;j1<4;j1++){
rasp=max(rasp,aux[i][j][j1]-v[i][j]);
}
}
}
cout<<rasp;
return 0;
}
