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 GET_MACRO(_1,_2,_3,_4,_5,_6,_7,_8,NAME,...) NAME
#define pr(...) cerr<< GET_MACRO(__VA_ARGS__,pr8,pr7,pr6,pr5,pr4,pr3,pr2,pr1)(__VA_ARGS__) <<endl
#define pr1(a) (#a)<<"="<<(a)<<" "
#define pr2(a,b) pr1(a)<<pr1(b)
#define pr3(a,b,c) pr1(a)<<pr2(b,c)
#define pr4(a,b,c,d) pr1(a)<<pr3(b,c,d)
#define pr5(a,b,c,d,e) pr1(a)<<pr4(b,c,d,e)
#define pr6(a,b,c,d,e,f) pr1(a)<<pr5(b,c,d,e,f)
#define pr7(a,b,c,d,e,f,g) pr1(a)<<pr6(b,c,d,e,f,g)
#define pr8(a,b,c,d,e,f,g,h) pr1(a)<<pr7(b,c,d,e,f,g,h)
#define prArr(a) {cerr<<(#a)<<"={";int i=0;for(auto t:(a))cerr<<(i++?", ":"")<<t;cerr<<"}"<<endl;}
using namespace std;
using Int = long long;
using _int = int;
using ll = long long;
using Double = long double;
const Int INF = (1LL<<60)+1e9; // ~ 1.15 * 1e18
const Int mod = (1e9)+7;
const Double EPS = 1e-8;
const Double PI = 6.0 * asin((Double)0.5);
using P = pair<Int,Int>;
template<class T> T Max(T &a,T b){return a=max(a,b);}
template<class T> T Min(T &a,T b){return a=min(a,b);}
template<class T1, class T2> ostream& operator<<(ostream& o,pair<T1,T2> p){return o<<"("<<p.first<<","<<p.second<<")";}
template<class T1, class T2, class T3> ostream& operator<<(ostream& o,tuple<T1,T2,T3> t){
  return o<<"("<<get<0>(t)<<","<<get<1>(t)<<","<<get<2>(t)<<")";}
template<class T1, class T2> istream& operator>>(istream& i,pair<T1,T2> &p){return i>>p.first>>p.second;}
template<class T> ostream& operator<<(ostream& o,vector<T> a){Int i=0;for(T t:a)o<<(i++?" ":"")<<t;return o;}
template<class T> istream& operator>>(istream& i,vector<T> &a){for(T &t:a)i>>t;return i;}

Int h, w;
vector<vector<Int> > mp;

Int calc(Int y,Int x, Int n,Int m){
  if(y + n - 1 >= h || x + m - 1 >= w) return -INF;

  Int height = INF;
  for(int i=0;i<n;i++) Min(height, mp[y + i][x]);
  for(int i=0;i<n;i++) Min(height, mp[y + i][x + m - 1]);
  for(int i=0;i<m;i++) Min(height, mp[y][x + i]);
  for(int i=0;i<m;i++) Min(height, mp[y + n - 1][x + i]);

  Int sum = 0;
  for(int i=0;i<n-2;i++)
    for(int j=0;j<m-2;j++){
      int num = mp[y + 1 + i][x + 1 + j];
      if(num >= height) return -INF;
      sum += (height - num);
    }
  return sum;
}

signed main(){
  srand((unsigned)time(NULL));
  cin.tie(0);
  ios_base::sync_with_stdio(0);
  cout << fixed << setprecision(12);

  while(1){
    cin>>h>>w;
    if(h == 0 && w == 0) break;
    mp.clear();
    mp.resize(h, vector<Int>(w));
    
    cin>>mp;
    Int ans = 0;
    for(int i=0;i<h;i++)
      for(int j=0;j<w;j++)
	for(int n=3;n<=h;n++)
	  for(int m=3;m<=w;m++) Max(ans, calc(i, j, n, m));

    cout<<ans<<endl;
  }
  
  return 0;
}

C++: #include<iostream>
#include<iomanip>
#include<cmath>
#include<cstdlib>
#include<cstring>
#include<string>
#include<algorithm>
#include<vector>
#include<queue>
#include<numeric>
using namespace std;

#define R(i,s,n) for(int i=s;i<n;i++)
#define D(i,n,s) for(int i=n-1;i>=s;i--)
typedef pair<int,int> P;

const int MAX_DW = 10;
const int INF = 1e+9;

int D,W;
int ike[MAX_DW][MAX_DW];
int mn,mx,tmp;

void solve();

int main() {

  while(cin>>D>>W && (D || W)) {
    R(i,0,D) {
      R(j,0,W) cin>>ike[i][j];
    }

    solve();
  }

  return 0;
}

void solve() {
  mx = 0;

  R(high,3,D+1) { //池の縦の長さ
    R(wide,3,W+1) { //池の横の長さ
      R(shigh,0,D-high+1) { //池の始点の縦の位置
        R(swide,0,W-wide+1) { //池の始点の横の位置
          //変数初期化
          tmp = 0;
          mn = INF;

          //周りのmin算出
          R(i,0,high) {
            R(j,0,wide) {
              if(i==0 || i==high-1 || j==0 || j==wide-1) mn = min(mn,ike[shigh+i][swide+j]);
            }
          }
          if(mn == 0) continue;

          //池の中探索
          R(i,1,high-1) {
            R(j,1,wide-1) {
              if(mn>ike[shigh+i][swide+j]) tmp+=(mn-ike[shigh+i][swide+j]);
              else goto CONT;
            }
          }
          if(tmp>mx) mx = tmp;  //更新
          CONT: ;
        } //swideのループ
      } //shighのループ
    } //wideのループ
  } //highのループ

  cout<<mx<<endl;
}