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 <iostream>
using namespace std;
int h,w,dp[10][10],L,ok,cnt,ans;
int main(void){
    while(1){
    cin>>h>>w;
    if(h==0&&w==0)return 0;
    ans=0;
    for(int i=0;i<h;i++){
        for(int j=0;j<w;j++){
            cin>>dp[i][j];
        }
    }
    for(int x1=1;x1<h-1;x1++){
        for(int x2=x1;x2<h-1;x2++){
            for(int y1=1;y1<w-1;y1++){
                for(int y2=y1;y2<w-1;y2++){
                    L=10;
                    ok=1;
                    cnt=0;
                    for(int i=x1-1;i<=x2+1;i++){
                        L=min(L,dp[i][y1-1]);
                        L=min(L,dp[i][y2+1]);
                    }
                    for(int i=y1-1;i<=y2+1;i++){
                        L=min(L,dp[x1-1][i]);
                        L=min(L,dp[x2+1][i]);
                    }
                    for(int i=x1;i<=x2;i++){
                        for(int j=y1;j<=y2;j++){
                            if(L<=dp[i][j])ok=0;
                            cnt+=dp[i][j];
                        }
                    }
                    if(ok){
                        ans=max(ans,(x2-x1+1)*(y2-y1+1)*L-cnt);
                    }
                }
            }
        }
    }
    cout<<ans<<endl;
    }
}

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

#define INF_LL (int64)1e18
#define INF (int32)1e9
#define REP(i, n) for(int64 i = 0;i < (n);i++)
#define FOR(i, a, b) for(int64 i = (a);i < (b);i++)
#define all(x) x.begin(),x.end()
#define fs first
#define sc second

using int32 = int_fast32_t;
using uint32 = uint_fast32_t;
using int64 = int_fast64_t;
using uint64 = uint_fast64_t;
using PII = pair<int32, int32>;
using PLL = pair<int64, int64>;

const double eps = 1e-10;

template<typename A, typename B>inline void chmin(A &a, B b){if(a > b) a = b;}
template<typename A, typename B>inline void chmax(A &a, B b){if(a < b) a = b;}

template<typename T>
vector<T> make_v(size_t a){return vector<T>(a);}

template<typename T,typename... Ts>
auto make_v(size_t a,Ts... ts){
  return vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));
}

template<typename T,typename U,typename... V>
typename enable_if<is_same<T, U>::value!=0>::type
fill_v(U &u,const V... v){u=U(v...);}

template<typename T,typename U,typename... V>
typename enable_if<is_same<T, U>::value==0>::type
fill_v(U &u,const V... v){
  for(auto &e:u) fill_v<T>(e,v...);
}

int main(void) {
	int64 h, w;
	while (cin >> h >> w && h+w) {
		auto f = make_v<int64>(h, w);
		REP(i, h) REP(j, w) cin >> f[i][j];
		int64 res = 0;
		REP(lu_y, h) {
			REP(lu_x, w) {
				FOR(rd_y, lu_y+2, h) {
					FOR(rd_x, lu_x+2, w) {
						int64 mini = INF, maxi = 0, sum = 0;
						FOR(y, lu_y, rd_y+1) {
							FOR(x, lu_x, rd_x+1) {
								if (y == lu_y || y == rd_y || x == lu_x || x == rd_x)
									mini = min(mini, f[y][x]);
								else {
									maxi = max(maxi, f[y][x]);
									sum += f[y][x];
								}
							}
						}
						if (maxi < mini)
							res = max(res, (rd_x-lu_x-1)*(rd_y-lu_y-1)-sum);
					}
				}
			}
		}
		cout << res << endl;
	}
}

C++: #include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for(int i = 0; i < n; ++i)
#define rep2(i, a, b) for(int i = (a); i <= (b); ++i)

main() {
    while(1) {
        int h, w;
        cin >> h >> w;
        if(!h) return 0;
        vector<vector<int>> a(h, vector<int>(w));
        rep(i, h) rep(j, w) cin >> a[i][j];
        int ans = 0;
        rep(i, h) rep2(ii, i, h - 1) rep(j, w) rep2(jj, j, w - 1) {
            int d = 0;
            if(i + 1 >= ii or j + 1 >= jj) continue;
            rep2(iii, i + 1, ii - 1) {
                rep2(jjj, j + 1, jj - 1) { d = max(d, a[iii][jjj]); }
            }
            int D = INT_MAX;
            rep2(jjj, j, jj) D = min({D, a[i][jjj], a[ii][jjj]});
            rep2(iii, i, ii) D = min({a[iii][j], a[iii][jj], D});
            if(D <= d) continue;
            int now = 0;
            rep2(iii, i + 1, ii - 1) rep2(jjj, j + 1, jj - 1) now += D - a[iii][jjj];
            ans = max(ans, now);
        }
        cout << ans << endl;
    }
}