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;

#pragma GCC optimize("Ofast")
#define rep(i,a,n) for(int i=a; i<n; i++)
typedef long long ll;
typedef pair<int,int> P;
const ll MOD = (int)1e9+7;
const ll INF = MOD*MOD;
const ll powll = 1LL<<1;

int main(void){
    int h,w;
    while(1){
        cin >> h >> w;
        if(h ==  0){
            break;
        }else
        {
            //in
            int ike[h][w];
            rep(i,0,h) {
                rep(j,0,w) {
                    cin >> ike[i][j];
                }
            }
            int ans = 0;
            rep(sx,0,w-2){
                rep(sy,0,h-2){
                    rep(gx,sx+2,w){
                        rep(gy,sy+2,h){
                            int innerSum = 0;
                            int innerH = 0;
                            int outerH = MOD;
                            rep(innerX,sx,gx+1){
                                rep(innerY,sy,gy+1){
                                    if(innerX == sx || innerX == gx){
                                        outerH = min(outerH, ike[innerY][innerX]);
                                    }else if(innerY == sy || innerY == gy){
                                        outerH = min(outerH, ike[innerY][innerX]);
                                    }else{
                                        innerH = max(innerH, ike[innerY][innerX]);
                                    }
                                }
                            }
                            /*
                            cout <<sx << " "<< sy << " ";
                            cout <<gx << " " << gy << " ";
                            cout << innerH << " " << outerH << "\n";
                            */
                            rep(innerX,sx,gx+1){
                                rep(innerY,sy,gy+1){
                                    if(innerX == sx || innerX == gx){
                                    }else if(innerY == sy || innerY == gy){
                                    }else{
                                        innerSum += max(0,outerH - ike[innerY][innerX]);
                                    }
                                }
                            }
                            
                            //  cout << "outerSum= " << innerSum << "\n";
                            
                            if(innerH < outerH){
                                ans = max(ans,innerSum);
                            }
                        }
                    }
                }
                
            }
            cout << ans << "\n";
        }

    }
    
}

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

int main()
{
	int d, w;
	while (cin >> d >> w, d | w) {
		vector<vector<int>> e(d, vector<int>(w));
		for (int i = 0; i < d; i++) {
			for (int j = 0; j < w; j++) {
				cin >> e[i][j];
			}
		}
		int res = 0;
		for (int i = 0; i < d; i++) {
			for (int j = i + 3; j <= d; j++) {
				for (int k = 0; k < w; k++) {
					for (int l = k + 3; l <= w; l++) {
						int ma = 0, mi = 10;
						for (int x = i; x < j; x++) {
							for (int y = k; y < l; y++) {
								if (x == i || x == j - 1 || y == k || y == l - 1) {
									mi = min(mi, e[x][y]);
								}
								else {
									ma = max(ma, e[x][y]);
								}
							}
						}
						if (ma < mi) {
							int sum = 0;
							for (int x = i + 1; x < j - 1; x++) {
								for (int y = k + 1; y < l - 1; y++) {
									sum += mi - e[x][y];
								}
							}
							res = max(res, sum);
						}
					}
				}
			}
		}
		cout << res << endl;
	}
	return 0;
}

C++: #define _USE_MATH_DEFINES

#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <cmath>
#include <algorithm>
#include <vector>
#include <queue>
#include <map>

using namespace std;

int main(){
	
	while(true){
		int H, W;
		cin >> H >> W;
		if(H == 0 && W == 0){
			break;
		}
		int a[20][20];
		for(int i = 0; i < H; i++){
			for(int j = 0; j < W; j++){
				cin >> a[i][j];
			}
		}
		int ans = 0;
		for(int sy = 0; sy < H; sy++){
			for(int gy = sy + 2; gy < H; gy++){
				for(int sx = 0; sx < W; sx++){
					for(int gx = sx + 2; gx < W; gx++){
						int mini = 1000;
						int maxi = 0;
						int sum = 0;
						for(int i = sy; i <= gy; i++){
							for(int j = sx; j <= gx; j++){
								if(i == sy || i == gy || j == sx || j == gx){
									mini = min(mini, a[i][j]);
								}else{
									sum += a[i][j];
									maxi = max(maxi, a[i][j]);
								}
							}
						}
						if(mini - maxi > 0){
							ans = max(ans, mini * (gx - sx - 1) * (gy - sy - 1) - sum);
						}
					}
				}
			}
		}
		cout << ans << endl;
	}
	
	return 0;
	
}