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>
using namespace std;
/*{{{*/  //template
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define rrep(i,n) for(int i=(n)-1;i>=0;i--)
constexpr int INF = numeric_limits<int>::max()/2;
constexpr long long LINF = numeric_limits<long long>::max()/3;
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define all(v) (v).begin(),(v).end()
#define sz(x) (int)(x).size()
#define debug(x) cerr<<#x<<":"<<x<<endl
#define debug2(x,y) cerr<<#x<<","<<#y":"<<x<<","<<y<<endl
//struct fin{ fin(){ cin.tie(0); ios::sync_with_stdio(false); } } fin_;
struct Double{ double d; explicit Double(double x) : d(x){} };
ostream& operator<<(ostream& os,const Double x){ os << fixed << setprecision(20) << x.d; return os; }
template<typename T> ostream& operator<<(ostream& os,const vector<T>& vec){ os << "["; for(const auto& v : vec){ os << v << ","; } os << "]"; return os; }
template<typename T,typename U> ostream& operator<<(ostream& os, const map<T,U>& mp){ os << "{"; for(auto& p : mp){ os << p << ","; } os << "}"; return os; }
template<typename T,typename U> ostream& operator<<(ostream& os,const pair<T,U>& p){ os << "(" << p.first << ","<< p.second <<")"; return os; }
template<typename T> ostream& operator<<(ostream& os,const set<T>& st){ os<<"{"; for(T v:st) os<<v<<","; os <<"}"; return os; }
template<typename T,typename U> inline void chmax(T &x,U y){ if(y>x) x = y; }
template<typename T,typename U> inline void chmin(T &x,U y){ if(y<x) x = y; }
using ll = long long;
using ull = unsigned long long;
using pii = std::pair<int,int>;
using vi = std::vector<int>;
typedef vector<vi> vvi;
ll gcd(ll a,ll b){ if(b==0) return a; else return gcd(b,a%b); }
constexpr ll TEN(int n) { return (n == 0) ? 1 : 10 * TEN(n - 1); }
//constexpr double eps = 1e-14; 
constexpr double eps = 1e-10; 
constexpr ll mod = 1e9+7;
const int dx[]={1,0,-1,0} ,dy[] = {0,1,0,-1};
/*}}}*/

int h,w;

void solve(){
    vector<vector<int>> a(h,vector<int>(w));
    rep(i,h) rep(j,w) cin >> a[i][j];

    int ans = 0;
    for(int x1=0;x1<h;x1++){
        for(int y1=0;y1<w;y1++){
            for(int x2=x1;x2<h;x2++){
                for(int y2=y1;y2<w;y2++){
                    int mn = 100;
                    for(int y=y1;y<=y2;y++){
                        mn = min({mn,a[x1][y],a[x2][y]});
                    }
                    for(int x=x1;x<=x2;x++){
                        mn = min({mn,a[x][y1],a[x][y2]});
                    }

                    bool ok = true;
                    int cnt = 0;
                    for(int x=x1+1;x<x2;x++){
                        for(int y=y1+1;y<y2;y++){
                            if(a[x][y] >= mn){
                                ok = false;
                                break;
                            }
                            cnt += mn - a[x][y];
                        }
                    }

                    if(!ok) continue;

                    ans = max(ans,cnt);
                }
            }
        }
    }
    cout << ans << endl;
}

int main(){
    while(cin >> h >> w){
        if(!h and !w) break;
        solve();
    }
}

C++: #include <iostream>

using namespace std;

int h, w;
int a[15][15];
int M;

int check(int sx, int sy, int tx, int ty)
{
	int minbd = 10, maxin = 0;
	for(int x = sx; x <= tx; x++){
		for(int y = sy; y <= ty; y++){
			if(x == sx || x == tx || y == sy || y == ty){
				minbd = min(minbd, a[x][y]);
			}
			else{
				maxin = max(maxin, a[x][y]);
			}
		}
	}
	if(minbd <= maxin) return 0;
	return minbd;
}

int calc(int sx, int sy, int tx, int ty, int maxbd)
{
	int ret = 0;
	for(int x = sx+1; x < tx; x++){
		for(int y = sy+1; y < ty; y++){
			ret += maxbd - a[x][y];
		}
	}
	return ret;
}

int main(void)
{
	while(1){
		cin >> h >> w;
		if(h == 0 && w == 0) break;
		for(int y = 1; y <= h; y++){
			for(int x = 1; x <= w; x++){
				cin >> a[x][y];
			}
		}
		
		int ans = 0, bd;
		for(int sx = 1; sx <= w-2; sx++){
			for(int sy = 1; sy <= h-2; sy++){
				for(int tx = 3; tx <= w; tx++){
					for(int ty = 3; ty <= h; ty++){
						if(tx < sx+2 || ty < sy+2) continue;
						if(!(bd = check(sx, sy, tx, ty))) continue;
						ans = max(ans, calc(sx, sy, tx, ty, bd));
					}
				}
			}
		}
		cout << ans << endl;
	}
	
	return 0;
}