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;

using i64 = int64_t;

int garden[12][12]={0};

void init(){
    for(int i=0;i<=10;++i){
        for(int j=0;j<=10;++j)
            garden[i][j] = 0;
    }
}

int main(){
    int d, w;
    while(cin >> d >> w, d != 0){
        init();
        for(int i=0;i<d;++i){
            for(int j=0;j<w;++j){
                cin >> garden[i][j];
            }
        }

        int ans = 0;
        for(int top=0;top<d;++top){
            for(int left=0;left<w;++left){
                for(int bottom=top+2;bottom<d;++bottom){
                    for(int right=left+2;right<w;++right){
                        int mini = 11;
                        for(int i=left;i<=right;++i){
                            mini = min(mini, garden[top][i]);
                            mini = min(mini, garden[bottom][i]);
                        }
                        for(int i=top;i<=bottom;++i){
                            mini = min(mini, garden[i][left]);
                            mini = min(mini, garden[i][right]);
                        }
                        bool ok = true;
                        int sum = 0;
                        for(int i=top+1;i<bottom;++i){
                            for(int j=left+1;j<right;++j){
                                if(garden[i][j] >= mini){
                                    ok = false;
                                    break;
                                }
                                sum += mini - garden[i][j];
                            }
                            if(!ok)break;
                        }
                        if(ok)ans = max(ans, sum);
                    }
                }
            }
        }
        cout << ans << endl;
    }

    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
using ll = int64_t;
template <typename T> using V = vector<T>;

struct Solver {
    ll H, W;
    V<V<ll>> vs;
    Solver() {
        cin >> H >> W;
        if(H + W) {
            vs = V<V<ll>>(H, V<ll>(W, 0));
            for(auto &v : vs) for(auto &ele : v) cin >> ele;
        }
    }

    ll calc(ll uh, ll dh, ll lw, ll rw) {
        ll lowest = 5e15;
        ll highest = 0;
        ll osum = 0;
        ll sum = 0;
        // cout << uh << ", " << dh << ", " << lw << ", " << rw << endl;
        for(ll h = uh; h < dh; h++) for(ll w = lw; w < rw; w++) {
            if(h == uh || h == dh - 1 || w == lw || w == rw - 1) {
                lowest = min(lowest, vs[h][w]);
            } else {
                highest = max(highest, vs[h][w]);
                sum += vs[h][w];
            }
        }
        // cout << highest << ", " << lowest << endl;
        if(highest >= lowest) return 0;
        ll ans = (dh - uh) * (rw - lw) * lowest - sum;
        ans -= ((dh - uh) + (rw - lw) - 2) * 2 * lowest;
        return ans;
    }
    
    bool solve() {
        if(!(H + W)) return false;
        ll ans = 0;
        for(ll lw = 0; lw < W; lw++) for(ll rw = lw + 3; rw <= W; rw++) {
            for(ll uh = 0; uh < H; uh++) for(ll dh = uh + 3; dh <= H; dh++) {
                ans = max(ans, calc(uh, dh, lw, rw));
            }
        }
        cout << ans << endl;
        return true;
    }
};

int main() {
    while(Solver().solve());
    return 0;
}