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;
typedef long long LL;
typedef pair<LL,LL> P;
const LL mod=1e9+7;
const LL LINF=1LL<<62;
const int INF=1<<17;

int main(){
    int d,w;
    while(cin >> d >> w){
        if(d==0&&w==0) break;
        int st[d][w];
        for(int i=0;i<d;i++){
            for(int j=0;j<w;j++){
                cin >> st[i][j];
            }
        }
        int ans=0;
        for(int i=0;i<d;i++){
            for(int j=0;j<w;j++){
                for(int y=3;y<=d;y++){
                    for(int x=3;x<=w;x++){
                        int mini=INF,maxi=-1;
                        if(d<i+y||w<j+x) continue;
                        int sum=0;
                        for(int s=0;s<y;s++){
                            for(int t=0;t<x;t++){
                                if(s==0||s==y-1||t==0||t==x-1){
                                    mini=min(mini,st[i+s][j+t]);
                                }
                                else{
                                    sum+=st[i+s][j+t];
                                    maxi=max(maxi,st[i+s][j+t]);
                                }
                            }
                        }
                    if(maxi<mini) ans=max(ans,mini*(x-2)*(y-2)-sum);
                    }
                }
            }
        }
        cout << ans << endl;
    }
    return 0;
}

C++: #include<iostream>
using namespace std;
int t[15][15];
int n,m;

int check(int a,int b,int c,int d){
	if(c-a<2 || d-b<2)return -1;
	int i,j,k;
	int p,q,r;//min_edge max_inter sum
	p=100,q=-1,r=0;
	for(i=a;i<=c;i++){
		for(j=b;j<=d;j++){
			if(a<i && i<c && b<j && j<d){
				if(q<t[i][j])q=t[i][j];
				r+=t[i][j];
			}else if(t[i][j]<p)p=t[i][j];
		}
	}
	if(p<=q)return -1;
	return p*(c-a-1)*(d-b-1)-r;
}


int main(){
	int i,j,k,l;
	int a,b,c;
	int s=0;
	while(cin>>n>>m){
		if(!n)break;
		for(i=0;i<n;i++){
			for(j=0;j<m;j++){
				cin>>t[i][j];
			}
		}
		s=0;
		for(i=0;i<n;i++){
			for(j=0;j<m;j++){
				for(k=0;k<n;k++){
					for(l=0;l<m;l++){
						a=check(i,j,k,l);
						if(s<a)s=a;
					}
				}
			}
		}
		cout<<s<<endl;
	}
}

C++: #include <iostream>
#include <cstdio>
using namespace std;

int d, w;
int cap = 0;
int e[10][10];

int hight_of_ike(int sx, int sy, int col, int row) {
    int suii = e[sy][sx];
    for (int y = sy; y <= sy + col; ++y) {
        for (int x = sx; x <= sx + row; ++x) {
            suii = max(suii, e[y][x]);
        }
    }
    return suii;
}

int hight_of_sto(int sx, int sy, int col, int row) {
    int hight = e[sx][sy];
    for (int y = sy; y <= sy + col; ++y) {
        for (int x = sx; x <= sx + row; ++x) {
            if (y > sy && y < sy + col && x > sx && x < sx + row) continue;
            hight = min(hight, e[y][x]);
        }
    }
    return hight;
}

int get_cap(int sto, int sx, int sy, int col, int row) {
    int tmp = 0;
    for (int y = sy; y <= sy + col; ++y) {
        for (int x = sx; x <= sx + row; ++x) {
            tmp += sto - e[y][x];
        }
    }
    return tmp;
}

int main() {
    while(cin >> d >> w, d||w) {
        cap = 0;
        for (int y = 0; y < d; ++y) {
            for (int x = 0; x < w; ++x) {
                cin >> e[y][x];
            }
        }
        for (int sy = 1; sy < d - 1; ++sy) {
            for (int sx = 1; sx < w - 1; ++sx) {
                for (int col = 0; sy + col < d - 1; ++col) {
                    for (int row = 0; sx + row < w - 1; ++row) {
                        int ike = hight_of_ike(sx, sy, col, row);
                        int sto = hight_of_sto(sx-1, sy-1, col+2, row+2);
                        if (sto - ike > 0) {
                            cap = max(cap, get_cap(sto, sx, sy, col, row));
                        }
                    }
                }
            }
        }
        cout << cap << endl;
    }
    return 0;
}