Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

func main() {
	io := NewIo()
	defer io.Flush()
	for {
		d, w := io.NextInt(), io.NextInt()
		if d == 0 {
			break
		}
		e := make([][]int, d)
		for i := 0; i < d; i++ {
			e[i] = make([]int, w)
			for j := 0; j < w; j++ {
				e[i][j] = io.NextInt()
			}
		}
		ans := 0
		for i := 0; i < d-2; i++ {
			for j := 0; j < w-2; j++ {
				for k := i + 2; k < d; k++ {
					for l := j + 2; l < w; l++ {
						ans = intMax(vol(e, i, j, k, l), ans)
					}
				}
			}
		}
		io.Println(ans)
	}
}

func vol(e [][]int, a, b, c, d int) int {
	outer := 10
	for i := a; i <= c; i++ {
		outer = intMin(e[i][b], outer)
		outer = intMin(e[i][d], outer)
	}
	for j := b; j <= d; j++ {
		outer = intMin(e[a][j], outer)
		outer = intMin(e[c][j], outer)
	}
	a++
	b++
	vol := 0
	for i := a; i < c; i++ {
		for j := b; j < d; j++ {
			if e[i][j] >= outer {
				return 0
			}
			vol += outer - e[i][j]
		}
	}
	return vol
}

func intMax(a, b int) int {
	if a < b {
		return b
	}
	return a
}

func intMin(a, b int) int {
	if a > b {
		return b
	}
	return a
}

// I/O template
type Io struct {
	reader    *bufio.Reader
	writer    *bufio.Writer
	tokens    []string
	nextToken int
}

func NewIo() *Io {
	return &Io{
		reader: bufio.NewReader(os.Stdin),
		writer: bufio.NewWriter(os.Stdout),
	}
}

func (io *Io) Flush() {
	err := io.writer.Flush()
	if err != nil {
		panic(err)
	}
}

func (io *Io) NextLine() string {
	var buff []byte
	for {
		line, isPrefix, err := io.reader.ReadLine()
		if err != nil {
			panic(err)
		}
		buff = append(buff, line...)
		if !isPrefix {
			break
		}
	}
	return string(buff)
}

func (io *Io) Next() string {
	for io.nextToken >= len(io.tokens) {
		line := io.NextLine()
		io.tokens = strings.Fields(line)
		io.nextToken = 0
	}
	s := io.tokens[io.nextToken]
	io.nextToken++
	return s
}

func (io *Io) NextInt() int {
	i, err := strconv.Atoi(io.Next())
	if err != nil {
		panic(err)
	}
	return i
}

func (io *Io) NextFloat() float64 {
	i, err := strconv.ParseFloat(io.Next(), 64)
	if err != nil {
		panic(err)
	}
	return i
}

func (io *Io) Println(a ...interface{}) {
	fmt.Fprintln(io.writer, a...)
}

func (io *Io) Printf(format string, a ...interface{}) {
	fmt.Fprintf(io.writer, format, a...)
}

func (io *Io) PrintIntSlice(a []int) {
	b := []interface{}{}
	for _, x := range a {
		b = append(b, x)
	}
	io.Println(b...)
}

func (io *Io) PrintStringSlice(a []string) {
	b := []interface{}{}
	for _, x := range a {
		b = append(b, x)
	}
	io.Println(b...)
}

func Log(name string, value interface{}) {
	fmt.Fprintf(os.Stderr, "%s=%+v\n", name, value)
}

func ExampleIo() {
	io := NewIo()
	defer io.Flush()
	a := make([]int, 0, 3)
	a[0], a[1], a[2] = io.NextInt(), io.NextInt(), io.NextInt()
	io.Println(a)
	io.PrintIntSlice(a)
	Log("io", a)
}

C++: //#include <bits/stdc++.h>
//#include <stdio.h>
#include<iostream>
#include<cstdio>
#include<bitset>
#include<algorithm>
#include<vector>
#include<list>
#include<queue>
#include<stack>
#include<string>
#include<string.h>
#include<cmath>
#include<utility>
#include<functional>
#include<map>
#include<set>
#include<cctype>
#include<fstream>
 
 
#define FOR(i, a, b) for( int i=(a);i<=(b);i++)
#define RFOR(i, a, b) for( int i=(a);i>=(b);i--)
#define LFOR(i, a, b) for( long long int i=(a);i<=(b);i++)
#define LRFOR(i, a, b) for(long long int i=(a);i>=(b);i--)
#define MOD 1000000007
#define INF 1000000000 //2000000000
#define LINF 1000000000000000000 //9000000000000000000
#define PI 3.14159265358979
#define MAXI 7500000
 
using namespace std;
typedef long long int ll;
typedef pair< long long int, long long  int> P;
 
int dy[5] = { 0,0,1,-1,0 };
int dx[5] = { 1,-1,0,0,0 };
 
int main(void){
	while(1){
		bool flag=false;
		int d,w;
		int outline=INF;
		int maxi=0;
		int tmp=0;
		int e[11][11];

		cin>>d>>w;
		if(d==0&&w==0){
			break;
		}
		FOR(i,1,d){
			FOR(j,1,w){
				cin>>e[i][j];
			}
		}

		FOR(xf,1,w-2){
			FOR(yf,1,d-2){
				FOR(xe,xf+2,w){
					FOR(ye,yf+2,d){
						outline=INF;
						FOR(x,xf,xe){
							outline=min(outline,min(e[yf][x],e[ye][x]));
						}
						FOR(y,yf,ye){
							outline=min(outline,min(e[y][xf],e[y][xe]));
						}

						tmp=0;
						flag=false;
						FOR(x,xf+1,xe-1){
							FOR(y,yf+1,ye-1){
								if(e[y][x]<outline){
									tmp+=(outline-e[y][x]);
								}else{
									tmp=0;
									flag=true;
									break;
								}
							}
							if(flag){
								break;
							}
						}

						//cout<<xf<<" "<<xe<<" "<<yf<<" "<<ye<<" "<<tmp<<endl;

						maxi=max(maxi,tmp);

					}
				}
			}
		}

		cout<<maxi<<endl;

	}

}

C++: #include <bits/stdc++.h>
using namespace std;

// region template
#define rep(i, a, b) for (int i = (a); i < (b); ++i)
#define trav(a, x) for (auto &a : x)
#define all(x) begin(x), end(x)
#define sz(x) (ll)(x).size()
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef vector<int> vi;

ll gcd(ll a, ll b) { return __gcd(a, b); }

ll euclid(ll a, ll b, ll &x, ll &y) {
    if (b) {
        ll d = euclid(b, a % b, y, x);
        return y -= a / b * x, d;
    }
    return x = 1, y = 0, a;
}

typedef unsigned long long ull;
typedef long double ld;
ull mod_mul(ull a, ull b, ull M) {
    ll ret = a * b - M * ull(ld(a) * ld(b) / ld(M));
    return ret + M * (ret < 0) - M * (ret >= (ll)M);
}
ull mod_pow(ull b, ull e, ull mod) {
    ull ans = 1;
    for (; e; b = mod_mul(b, b, mod), e /= 2)
        if (e & 1)
            ans = mod_mul(ans, b, mod);
    return ans;
}

const ll mod = 1000000007;
struct Mod {
    ll x;
    Mod(ll xx) : x(xx) {}
    Mod operator+(Mod b) { return Mod((x + b.x) % mod); }
    Mod operator-(Mod b) { return Mod((x - b.x) % mod); }
    Mod operator*(Mod b) { return Mod((x * b.x) % mod); }
    Mod operator/(Mod b) { return *this * invert(b); }
    Mod invert(Mod a) {
        ll x, y, g = euclid(a.x, mod, x, y);
        assert(g == 1);
        return Mod((x + mod) % mod);
    }
    Mod operator^(ll e) {
        if (!e)
            return Mod(1);
        Mod r = *this ^ (e / 2);
        r = r * r;
        return e & 1 ? *this * r : r;
    }
};
// endregion

int main() {
    cin.sync_with_stdio(0);
    cin.tie(0);
    cin.exceptions(cin.failbit);

    for (;;) {
        int d, w; cin >> d >> w;
        if (!d) break;
        vector<vi> m(d, vi(w));

        rep(i, 0, d) rep(j, 0, w) cin >> m[i][j];

        int ans = 0;

        rep(i, 0, d) rep(j, 0, w) rep(k, i + 2, d) rep(l, j + 2, w) {
            
            int intsum = 0;
            int intmax = 0;
            int outmin = 100;

            for (int a = i; a <= k; a++)
                outmin = min(outmin, min(m[a][j], m[a][l]));
            for (int b = j; b <= l; b++)
                outmin = min(outmin, min(m[i][b], m[k][b]));

            for (int a = i + 1; a <= k - 1; a++) {
                for (int b = j + 1; b <= l - 1; b++) {
                    intsum += m[a][b];
                    intmax = max(intmax, m[a][b]);
                }
            }

            if (intmax < outmin) {
                ans = max(ans, (k - i - 1) * (l - j - 1) * outmin - intsum);

                // for (int a = i; a <= k; a++) {
                //     for (int b = j; b <= l; b++) {
                //         cout << m[a][b];
                //     }
                //     cout << endl;
                // }
                // cout << (k - i - 1) * (l - j - 1) * outmin - intsum << endl;
            }

        }

        cout << ans << endl;
        // cerr << ";;;;;;;;;;;;;;;;;;;" << endl;
    }
}