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++: /**
 *    author:  otera    
**/
#include<iostream>
#include<string> 
#include<cstdio>
#include<cstring>
#include<vector>
#include<cmath>
#include<algorithm> 
#include<functional>
#include<iomanip>
#include<queue>
#include<deque>
#include<ciso646>
#include<random>
#include<map>
#include<set>
#include<complex>
#include<bitset>
#include<stack>
#include<unordered_map>
#include<utility>
#include<cassert>
using namespace std;

//#define int long long
typedef long long ll;
typedef unsigned long long ul;
typedef unsigned int ui;
typedef long double ld;
const int inf=1e9+7;
const ll INF=1LL<<60 ;
const ll mod=1e9+7 ;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
typedef complex<ld> Point;
const ld eps = 1e-8;
const ld pi = acos(-1.0);
typedef pair<int, int> P;
typedef pair<ld, ld> LDP;
typedef pair<ll, ll> LP;
#define fr first
#define sc second
#define all(c) c.begin(),c.end()
#define pb push_back
#define debug(x)  cerr << #x << " = " << (x) << endl;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

void solve() {
	int d, w; 
    while(cin >> d >> w) {
        if(d == 0 && w == 0) break;
        vector<vector<int>> e(d, vector<int>(w));
        rep(i, d) {
            rep(j, w) {
                cin >> e[i][j];
            }
        }
        int ans = 0;
        rep(i, d) {
            for(int j = i + 2; j < d; ++ j) {
                rep(k, w) {
                    for(int l = k + 2; l < w; ++ l) {
                        int mi = inf;
                        for(int x = i; x <= j; ++ x) {
                            chmin(mi, e[x][k]);
                            chmin(mi, e[x][l]);
                        }
                        for(int y = k; y <= l; ++ y) {
                            chmin(mi, e[i][y]);
                            chmin(mi, e[j][y]);
                        }
                        int res = 0;
                        bool ok = 1;
                        for(int x = i + 1; x <= j - 1; ++ x) {
                            for(int y = k + 1; y <= l - 1; ++ y) {
                                if(e[x][y] < mi) res += (mi - e[x][y]);
                                else ok = 0;
                            }
                        }
                        if(ok) chmax(ans, res);
                    }
                }
            }
        }
        cout << ans << endl;
    }
}

signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	//cout << fixed << setprecision(10);
	//int t; cin >> t; rep(i, t)solve();
	solve();
    return 0;
}

C++: #include <bits/stdc++.h>

#define REP(i, n) for (int i = 0; i < n; i++)
#define ALL(obj) obj.begin(), obj.end()

const int iINF = 1e9;
const long long llINF = 1e18;
const int MOD = 1e9 + 7;

using namespace std;

template <typename T>
int getFormer(const vector<T> &vec, T x) {
    return upper_bound(vec.begin(), vec.end(), x) - vec.begin() - 1;
}

template <typename T>
int getLatter(const vector<T> &vec, T x) {
    return lower_bound(vec.begin(), vec.end(), x) - vec.begin();
}

int e[10][10];

//[lx, rx] [ty, dy]
int getCap(int lx, int rx, int ty, int dy) {
    int out = iINF, inside = 0;
    for (int i = lx; i <= rx; i++) {
        out = min(out, e[ty][i]);
        out = min(out, e[dy][i]);
    }
    for (int i = ty; i <= dy; i++) {
        out = min(out, e[i][lx]);
        out = min(out, e[i][rx]);
    }

    for (int x = lx + 1; x < rx; x++) {
        for (int y = ty + 1; y < dy; y++) {
            inside = max(inside, e[y][x]);
        }
    }

    if (out > inside) {
        int res = 0;
        for (int x = lx + 1; x < rx; x++) {
            for (int y = ty + 1; y < dy; y++) {
                res += (out - e[y][x]);
            }
        }
        return res;
    } else {
        return 0;
    }
}

void solve(int height, int width) {
    REP(i, height) { REP(j, width) cin >> e[i][j]; }
    int ans = 0;
    for (int lx = 0; lx < width - 2; lx++) {
        for (int rx = lx + 2; rx < width; rx++) {
            for (int ty = 0; ty < height - 2; ty++) {
                for (int dy = ty + 2; dy < height; dy++) {
                    ans = max(ans, getCap(lx, rx, ty, dy));
                }
            }
        }
    }
    cout << ans << endl;
}

int main() {
    int d, w;
    while (cin >> d >> w && d) {
        solve(d, w);
    }
}