#include "bits/stdc++.h"
using namespace std;
#define ll long long
#define endl '\n'
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define rep2(i,a,b) for(int i=int(a);i<int(b);i++)
#define pb emplace_back
#define all(x) (x).begin(),(x).end()
int mod=1e9+7;
int mod2=998244353;
const int INF=1e9;

signed main(){
	ll h,w;
	while(1){
		cin>>h>>w;
		if(h==0&&w==0)break;
		vector<vector<ll> > e(h,vector<ll>(w));
		rep(i,h){
			rep(j,w)cin>>e[i][j];
		}
		ll ans=0;
		rep(i,h-2){
			rep(j,w-2){
				rep2(k,2,h){
					rep2(l,2,w){
						ll high=10;
						rep2(ii,i,k+1){
							high=min(high,e[ii][j]);
							high=min(high,e[ii][l]);
						}
						rep2(jj,j,l+1){
							high=min(high,e[i][jj]);
							high=min(high,e[k][jj]);
						}
						//cout<<i<<j<<k<<l<<endl;
						//cout<<high<<endl;
						ll tmp=0;
						bool f=true;
						rep2(ii,i+1,k){
							rep2(jj,j+1,l){
								if(high<=e[ii][jj])f=false;
								tmp+=high-e[ii][jj];
							}
						}
						if(f)ans=max(ans,tmp);
					}
				}
			}
		}
		cout<<ans<<endl;
	}
}

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