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;

// macro
#define rep(i,n) for(i=0;i<n;i++)
#define ll long long
#define all(v) v.begin(), v.end()

// code starts
int main()
{
	int d,w;cin>>d>>w;
  while(d!=0&&w!=0)
  {
    vector<vector<int>> e(d,vector<int>(w));
    int i,j,k,l,m,n;
    int ans=0;
    rep(i,d)rep(j,w)cin>>e[i][j];
    rep(i,d)rep(j,w)
    {
      for(k=i+2;k<d;k++)for(l=j+2;l<w;l++)
      {
        int side=10;
        int inside=0;
        int sum_inside=0;
        for(m=i;m<=k;m++)for(n=j;n<=l;n++)
        {
          if(m==i||m==k||n==j||n==l)
          {
            side=min(side,e[m][n]);
          }
          else
          {
            inside=max(inside,e[m][n]);
            sum_inside+=e[m][n];
          }
        }
        if(side>inside)
        {
          ans=max(ans,side*(k-i-1)*(l-j-1)-sum_inside);
        }
      }
    }
    cout<<ans<<endl;
    cin>>d>>w;
  }
}

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

int d, w;
int cap = 0;
int e[10][10];

int hight_of_ike(int sx, int sy, int col, int row) {
    int suii = e[sy][sx];
    for (int y = sy; y <= sy + col; ++y) {
        for (int x = sx; x <= sx + row; ++x) {
            suii = max(suii, e[y][x]);
        }
    }
    return suii;
}

int hight_of_sto(int sx, int sy, int col, int row) {
    int hight = e[sy][sx];
    for (int y = sy; y <= sy + col; ++y) {
        for (int x = sx; x <= sx + row; ++x) {
            if (y > sy && y < sy + col && x > sx && x < sx + row) continue;
            hight = min(hight, e[y][x]);
        }
    }
    return hight;
}

int get_cap(int sto, int sx, int sy, int col, int row) {
    int tmp = 0;
    for (int y = sy; y <= sy + col; ++y) {
        for (int x = sx; x <= sx + row; ++x) {
            tmp += sto - e[y][x];
        }
    }
    return tmp;
}

int main() {
    while(cin >> d >> w, d||w) {
        cap = 0;
        for (int y = 0; y < d; ++y) {
            for (int x = 0; x < w; ++x) {
                cin >> e[y][x];
            }
        }
        for (int sy = 1; sy < d - 1; ++sy) {
            for (int sx = 1; sx < w - 1; ++sx) {
                for (int col = 0; sy + col < d - 1; ++col) {
                    for (int row = 0; sx + row < w - 1; ++row) {
                        int ike = hight_of_ike(sx, sy, col, row);
                        int sto = hight_of_sto(sx-1, sy-1, col+2, row+2);
                        if (sto - ike > 0) {
                            cap = max(cap, get_cap(sto, sx, sy, col, row));
                        }
                    }
                }
            }
        }
        cout << cap << endl;
    }
    return 0;
}

C++: /*  -*- coding: utf-8 -*-
 *
 * 1618.cc: A Garden with Ponds
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_H = 10;
const int MAX_W = 10;
const int INF = 1 << 30;

/* typedef */

/* global variables */

int flds[MAX_H][MAX_W];

/* subroutines */

inline void setmin(int &a, int b) { if (a > b) a = b; }
inline void setmax(int &a, int b) { if (a < b) a = b; }

/* main */

int main() {
  for (int h, w; scanf("%d%d", &h, &w) == 2 && h > 0;) {
    for (int y = 0; y < h; y++)
      for (int x = 0; x < w; x++) scanf("%d", &flds[y][x]);

    int maxc = 0;
    for (int y0 = 0; y0 < h; y0++)
      for (int y1 = y0 + 2; y1 < h; y1++)
	for (int x0 = 0; x0 < w; x0++)
	  for (int x1 = x0 + 2; x1 < w; x1++) {
	    int mino = INF, maxd = 0, dsum = 0;

	    for (int x = x0; x <= x1; x++) {
	      setmin(mino, flds[y0][x]);
	      setmin(mino, flds[y1][x]);
	    }

	    for (int y = y0 + 1; y < y1; y++) {
	      setmin(mino, flds[y][x0]);
	      setmin(mino, flds[y][x1]);

	      for (int x = x0 + 1; x < x1; x++) {
		int &d = flds[y][x];
		setmax(maxd, d);
		dsum += d;
	      }
	    }

	    if (mino > maxd)
	      setmax(maxc, mino * (y1 - y0 - 1) * (x1 - x0 - 1) - dsum);
	  }

    printf("%d\n", maxc);
  }
  return 0;
}