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 1e+18
#define int long long
using namespace std;

signed main(){
	int d,w;
	while(cin >> d >> w,w){
		int field[15][15],ans = 0;
		for(int i = 0;i < d;i++){
			for(int j = 0;j < w;j++){
				cin >> field[i][j];
			}
		}
		for(int i = 0;i < d;i++){
			for(int j = 0;j < w;j++){
				for(int k = i + 2;k < d;k++){
					for(int l = j + 2;l < w;l++){
						int inmax = 0,outmin = INF,sum = 0;
						for(int a = i;a <= k;a++){
							for(int b = j;b <= l;b++){
								if(a == i || a == k || b == j || b == l){
									outmin = min(outmin,field[a][b]);
								}else{
									inmax = max(inmax,field[a][b]);
								}
							}
						}
						if(inmax < outmin){
							for(int a = i + 1;a < k;a++){
								for(int b = j + 1;b < l;b++){
									sum += outmin - field[a][b];
								}
							}
						}
						ans = max(ans,sum);
					}
				}
			}
		}
		cout << ans << endl;
	}
}

C++: #include <iostream>
#include <string>
#include <algorithm>
#include <functional>
#include <vector>
#include <utility>
#include <cstring>
#include <iomanip>
#include <numeric>
#include <cmath>
#include <cassert>
#include <complex>
#define repi(i, x, n) for(int i = x; i < n; i++)
#define rep(i, n) repi(i, 0, n)
#define endl "\n"
using namespace std;
const int INF = 1<<30;
const int MOD = (int)1e9 + 7;
const int MAX_N = (int)1e5 + 5;
#define debug(x) cout << #x << ": " << x << endl
signed main(void)
{
    int h, w;
    while(cin >> h >> w, h or w)
    {
        int table[h][w];
        for(int i = 0; i < h; i++) for(int j = 0; j < w; j++) cin >> table[i][j];
        int ans = 0;
        for(int i = 0; i < h; i++)
        {
            for(int j = 0; j < w; j++)
            {
                for(int k = i + 2; k < h; k++)
                {
                    for(int l = j + 2; l < w; l++)
                    {
                        int minv = INF;
                        for(int t = j; t <= l; t++) minv = min(minv, table[i][t]);
                        for(int t = j; t <= l; t++) minv = min(minv, table[k][t]);

                        for(int t = i; t <= k; t++) minv = min(minv, table[t][j]);
                        for(int t = i; t <= k; t++) minv = min(minv, table[t][l]);

                        int maxv = 0, sum = 0;
                        for(int a = i + 1; a < k; a++)
                        {
                            for(int b = j + 1; b < l; b++)
                            {
                                maxv = max(maxv, table[a][b]);
                                sum += (minv - table[a][b]);
                            }
                        }
                        if(maxv < minv)
                        {
                            ans = max(ans, sum); 
                        }
                    }
                }
            }
        }
        cout << ans << endl;
    }
    return 0;
}