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>
#define INF 1e18
#define int long long
#define Rep(i, a, n) for (int i = (a); i < (n); i++)
#define Repr(i, n, a) for (int i = (n); i >= (a); i--)
#define rep(i, n) Rep(i, 0, n)
#define repr(i, n) Repr(i, n, 0)
#define all(a) (a).begin(), (a).end()
using namespace std;
typedef pair<int, int> P;
typedef pair<P, int> PP;
const int mod = 1000000007;

int D, W, field[10][10];

int calc(int a, int b, int c, int d)
{
    int MIN = INF, MAX = -INF;
    Rep(i, b, d + 1) MIN = min(MIN, field[a][i]);
    Rep(i, b, d + 1) MIN = min(MIN, field[c][i]);
    Rep(i, a, c + 1) MIN = min(MIN, field[i][b]);
    Rep(i, a, c + 1) MIN = min(MIN, field[i][d]);
    Rep(i, a + 1, c) Rep(j, b + 1, d) MAX = max(MAX, field[i][j]);
    if (MAX >= MIN)
        return 0;
    int res = 0;
    Rep(i, a + 1, c) Rep(j, b + 1, d) res += MIN - field[i][j];
    return res;
}

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);

    while (1)
    {
        cin >> D >> W;
        if (D == 0)
            break;
        rep(i, D) rep(j, W) cin >> field[i][j];
        int ans = 0;
        rep(i, D) rep(j, W) Rep(k, i + 1, D) Rep(l, j + 1, W) ans = max(ans, calc(i, j, k, l));
        cout << ans << endl;
    }
}

C++: #include <bits/stdc++.h>

using namespace std;
#define _for(i,j,N) for(int i = (j);i < (N);i++)
#define _rep(i,j,N) for(int i = (j);i <= (N);i++)
#define _dec(i,N,j) for(int i = (N-1);i >= (j);i--)
#define _rec(i,N,j) for(int i = (N);i >=(j);i--)
#define ALL(x) x.begin(),x.end()
#define MEM(a,n) memset(a,n,sizeof(a))
#define fst first
#define scd second
#define PB push_back
#define MP make_pair

typedef long long LL;
typedef long double LD;
typedef pair<int,int> pii;
typedef pair<LL,LL> pll;

int get_int(){int x;scanf("%d",&x);return x;}
LL get_ll(){LL x;scanf("%lld",&x);return x;}
double get_db(){double x;scanf("%lf",&x);return x;}

template<typename T> int chmin(T &a,T b){if(a > b){a = b;return 1;}else return 0;}
template<typename T> int chmax(T &a,T b){if(a < b){a = b;return 1;}else return 0;}
template<typename T>
ostream& operator<<(ostream& os,const vector<T>& v) {_for(i,0,v.size()) os << v[i] << " ";return os;}
template<typename T>
ostream& operator<<(ostream& os,const set<T>& v){for(auto a:v) os << a <<" ";return os;}
template<typename T1,typename T2>
ostream& operator<<(ostream& os,const pair<T1,T2>& v){os << v.fst <<" "<<v.scd << " ";return os;}
template<typename T1,typename T2>
ostream& operator<<(ostream& os,const map<T1,T2>& v){for(auto a:v) cout << a << endl;return os;}

static const int dx[8] = { 1,  0, -1,  0,  1, -1,  1, -1};
static const int dy[8] = { 0,  1,  0, -1,  1, -1, -1,  1};
const double pi  = acos(-1.0);
const double eps = 1e-8;
const LL  INF  = 0x3f3f3f3f3f3f3f3f;
const int inf  = 0x3f3f3f3f;
const int mod = 1e9+7;

int d,w;

int G[11][11];

bool get_input(){
    scanf("%d %d",&d,&w);
    if(!d && !w) return false;
    _for(i,0,d){
        _for(j,0,w){
            scanf("%d",&G[i][j]);
        }
    }
    return true;
}

int check(int x,int y,int x2,int y2){
    int minv = inf;
    int ok = 1;
    int ret = 0;

    _rep(i,x,x2){
        chmin(minv,G[i][y]);
        chmin(minv,G[i][y2]);
    }
    _rep(j,y,y2){
        chmin(minv,G[x][j]);
        chmin(minv,G[x2][j]);
    }

    _for(i,x+1,x2){
        _for(j,y+1,y2){
            if(G[i][j] >= minv) ok = 0;
            else ret += minv - G[i][j];
        }
    }



    if(ok)
        return ret;
    else return 0;
}

int main()
{
    while(get_input()){
        int ans = 0;

        _for(i,0,d) _for(j,0,w) _for(k,i+1,d) _for(l,j+1,w){
            chmax(ans,check(i,j,k,l));

        }
        cout << ans << endl;


    }
    return 0;
}