/*#include<iostream>
#include<vector>
#include<algorithm>
#include<string>
#include<cmath>
#include<map>
#include<cstdio>
#include<stack>
#include<queue>
#include<fstream>
#include<cstdio>
#include<deque>
#include<iomanip>
#include <random>

using namespace std;
#define ok1 printf("ok1\n");
#define ok2 printf("ok2\n");
#define M 1000000000000000000LL
#define rep(i,n) for(int i=0;i<n;i++)
#define REP(i,s,n) for(int i=(s);i<(n);i++)
#define repr(i,n) for(int i=n-1;i>=0;i--)
#define REPR(i,s,n) for(int i=(s);i>=(n);(i)--)
#define all(a) (a).begin(),(a).end()
#define reall(a) (a).rbegin(),(a).rend()
#define pb push_back
#define pf push_front
#define MIN(a,b) a=min((a),(b))
#define MAX(a,b) a=max((a),(b))
#define SIZE(v) (int)v.size()
const double pi = acos(-1.0);

typedef vector<int> vi;
typedef vector<string> vs;
typedef long long ll;
typedef vector<ll> vll;
typedef vector<vi> vvi;
typedef deque<ll> dll;
#define mod 1e9 + 7;

int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
	cout.tie(nullptr);
	cout.setf(ios::fixed);
	cout.precision(20);

	vs v;
	string s1, s2;
	vs cs1, cs2;
	while (true) {
		cin >> s1;
		if (s1 == ".") break;
		cin >> s2;
		ll sum = 0;
		if (s1 == s2) v.pb("IDENTICAL");
		else {
			rep(i, s1.size()) {
				rep(j, s1.size()) {
					if (i != j && s1[i] == '"' && s1[j] == '"') {
						cs1.pb(s1.substr(i + 1, j - 1));
						s1[i] = '0'; s1[j] = '0';
					}

				}
			}
			rep(i, s2.size()) {
				rep(j, s2.size()) {
					if (i != j && s2[i] == '"' && s2[j] == '"') {
						cs2.pb(s2.substr(i + 1, j - 1));
						s2[i] = '0'; s2[j] = '0';
					}

				}
			}
			rep(i, cs1.size()) {
				cout << cs1[i] << " " << cs2[i] << endl;
				if (cs1[i] != cs2[i]) sum++;
				if (sum == 2) break;
			}
			if (sum == 1) v.pb("CLOSE");
			else v.pb("DIFFERENT");
		}
	}
	rep(i, v.size()) cout << v[i] << endl;
	return 0;
}*/
#include<iostream>
#include<vector>
#include<algorithm>
#include<string>
#include<cmath>
#include<map>
#include<cstdio>
#include<stack>
#include<queue>
#include<fstream>
#include<cstdio>
#include<deque>
#include<iomanip>

using namespace std;
#define ok1 printf("ok1\n");
#define ok2 printf("ok2\n");
#define M 1000000000000000000LL
#define rep(i,n) for(int i=0;i<n;i++)
#define REP(i,s,n) for(int i=(s);i<(n);i++)
#define repr(i,n) for(int i=n-1;i>=0;i--)
#define REPR(i,s,n) for(int i=(s);i>=(n);(i)--)
#define all(a) (a).begin(),(a).end()
#define reall(a) (a).rbegin(),(a).rend()
#define pb push_back
#define pf push_front
#define MIN(a,b) a=min((a),(b))
#define MAX(a,b) a=max((a),(b))
#define SIZE(v) (int)v.size()
const double pi = acos(-1.0);

typedef vector<int> vi;
typedef vector<string> vs;
typedef long long ll;
typedef vector<ll> vll;
typedef vector<vi> vvi;
typedef deque<ll> dll;
#define mod 1e9 + 7;

int main()
{
	ios_base::sync_with_stdio(false);

	int h, w;
	int s[100][100];
	while (cin >> h >> w) {
		if (!h) break;
		rep(i, h) {
			rep(j, w) {
				cin >> s[i][j];
			}
		}
		int ans = 0;
		rep(a, h)rep(b, w)rep(c, h)rep(d, w) {
			if (c - a < 2 || d - b < 2) continue;
			int sh = 100, nh = 0, mn = 100;
			REP(i, a, c + 1)REP(j, b, d + 1) {
				if (i == a || j == b || i == c || j == d) sh = min(sh, s[i][j]);
				else nh = max(nh, s[i][j]);
			}
			if (sh <= nh)continue;
			int sum = 0;
			REP(i, a, c + 1)REP(j, b, d + 1) {
				if (i == a || j == b || i == c || j == d)continue;
				sum += (sh - s[i][j]);
			}
			ans = max(ans, sum);
		}
		cout << ans << endl;
	}
	return 0;
}



Measured memory_bytes: 3144