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<iostream>
#include<vector>
#include<algorithm>
#include<string>
#include<cmath>
#include<map>
#include<cstdio>
#include<stack>
#include<queue>
#include<fstream>
#include<cstdio>
#include<deque>
#include<iomanip>
#include <random>

using namespace std;
#define ok1 printf("ok1\n");
#define ok2 printf("ok2\n");
#define M 1000000000000000000LL
#define rep(i,n) for(int i=0;i<n;i++)
#define REP(i,s,n) for(int i=(s);i<(n);i++)
#define repr(i,n) for(int i=n-1;i>=0;i--)
#define REPR(i,s,n) for(int i=(s);i>=(n);(i)--)
#define all(a) (a).begin(),(a).end()
#define reall(a) (a).rbegin(),(a).rend()
#define pb push_back
#define pf push_front
#define MIN(a,b) a=min((a),(b))
#define MAX(a,b) a=max((a),(b))
#define SIZE(v) (int)v.size()
const double pi = acos(-1.0);

typedef vector<int> vi;
typedef vector<string> vs;
typedef long long ll;
typedef vector<ll> vll;
typedef vector<vi> vvi;
typedef deque<ll> dll;
#define mod 1e9 + 7;

int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
	cout.tie(nullptr);
	cout.setf(ios::fixed);
	cout.precision(20);

	vs v;
	string s1, s2;
	vs cs1, cs2;
	while (true) {
		cin >> s1;
		if (s1 == ".") break;
		cin >> s2;
		ll sum = 0;
		if (s1 == s2) v.pb("IDENTICAL");
		else {
			rep(i, s1.size()) {
				rep(j, s1.size()) {
					if (i != j && s1[i] == '"' && s1[j] == '"') {
						cs1.pb(s1.substr(i + 1, j - 1));
						s1[i] = '0'; s1[j] = '0';
					}

				}
			}
			rep(i, s2.size()) {
				rep(j, s2.size()) {
					if (i != j && s2[i] == '"' && s2[j] == '"') {
						cs2.pb(s2.substr(i + 1, j - 1));
						s2[i] = '0'; s2[j] = '0';
					}

				}
			}
			rep(i, cs1.size()) {
				cout << cs1[i] << " " << cs2[i] << endl;
				if (cs1[i] != cs2[i]) sum++;
				if (sum == 2) break;
			}
			if (sum == 1) v.pb("CLOSE");
			else v.pb("DIFFERENT");
		}
	}
	rep(i, v.size()) cout << v[i] << endl;
	return 0;
}*/
#include<iostream>
#include<vector>
#include<algorithm>
#include<string>
#include<cmath>
#include<map>
#include<cstdio>
#include<stack>
#include<queue>
#include<fstream>
#include<cstdio>
#include<deque>
#include<iomanip>

using namespace std;
#define ok1 printf("ok1\n");
#define ok2 printf("ok2\n");
#define M 1000000000000000000LL
#define rep(i,n) for(int i=0;i<n;i++)
#define REP(i,s,n) for(int i=(s);i<(n);i++)
#define repr(i,n) for(int i=n-1;i>=0;i--)
#define REPR(i,s,n) for(int i=(s);i>=(n);(i)--)
#define all(a) (a).begin(),(a).end()
#define reall(a) (a).rbegin(),(a).rend()
#define pb push_back
#define pf push_front
#define MIN(a,b) a=min((a),(b))
#define MAX(a,b) a=max((a),(b))
#define SIZE(v) (int)v.size()
const double pi = acos(-1.0);

typedef vector<int> vi;
typedef vector<string> vs;
typedef long long ll;
typedef vector<ll> vll;
typedef vector<vi> vvi;
typedef deque<ll> dll;
#define mod 1e9 + 7;

int main()
{
	ios_base::sync_with_stdio(false);

	int h, w;
	int s[100][100];
	while (cin >> h >> w) {
		if (!h) break;
		rep(i, h) {
			rep(j, w) {
				cin >> s[i][j];
			}
		}
		int ans = 0;
		rep(a, h)rep(b, w)rep(c, h)rep(d, w) {
			if (c - a < 2 || d - b < 2) continue;
			int sh = 100, nh = 0, mn = 100;
			REP(i, a, c + 1)REP(j, b, d + 1) {
				if (i == a || j == b || i == c || j == d) sh = min(sh, s[i][j]);
				else nh = max(nh, s[i][j]);
			}
			if (sh <= nh)continue;
			int sum = 0;
			REP(i, a, c + 1)REP(j, b, d + 1) {
				if (i == a || j == b || i == c || j == d)continue;
				sum += (sh - s[i][j]);
			}
			ans = max(ans, sum);
		}
		cout << ans << endl;
	}
	return 0;
}

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


int canSpace(int sx, int sy, int gx, int gy, const vector<vector<int>>& e){
    int high = 100000;
    for (int i = sx; i <= gx; ++i) {
        high = min(high, e[i][sy]);
        high = min(high, e[i][gy]);
    }
    for (int i = sy; i <= gy; ++i) {
        high = min(high, e[sx][i]);
        high = min(high, e[gx][i]);
    }
    int space = 0;
    for (int i = sx + 1; i < gx; ++i) {
        for (int j = sy + 1; j < gy; ++j) {
            int sp = high - e[i][j];
            if(sp <= 0) return 0;
            space += sp;
        }
    }
    return space;
}

int main() {
    int d, w;
    while(1) {
        cin >> d >> w;
        if(d == 0 && w == 0) break;
        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 maxSpace = 0;
        for (int sx = 0; sx < d; ++sx) {
            for (int sy = 0; sy < w; ++sy) {
                for (int gx = sx + 2; gx < d; ++gx) {
                    for (int gy = sy + 2; gy < w; ++gy) {
                        maxSpace = max(maxSpace, canSpace(sx, sy, gx, gy, e));
                    }
                }
            }
        }
        cout << maxSpace << '\n';
    }

}