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;

int H, W;

int main() {
    int maximum, map[10][10], tmp_sea_max, tmp_wall_min, tmp;

    while (true) {
        scanf("%d %d", &H, &W);
        if (H == 0 && W == 0) break;

        for (int i = 0; i < H; i++) {
            for (int k = 0; k < W; k++) scanf("%d", &map[i][k]);
        }

        maximum = 0;

        for (int sea_left = 1; sea_left <= W - 2; sea_left++) {
            for (int sea_right = sea_left; sea_right <= W - 2; sea_right++) {
                for (int sea_top = 1; sea_top <= H - 2; sea_top++) {
                    for (int sea_bottom = sea_top; sea_bottom <= H - 2; sea_bottom++) {
                        tmp_sea_max = 0;
                        for (int row = sea_top; row <= sea_bottom; row++) {
                            for (int col = sea_left; col <= sea_right; col++) {
                                tmp_sea_max = max(tmp_sea_max, map[row][col]);
                            }
                        }

                        tmp_wall_min = 100;
                        for (int col = sea_left - 1; col <= sea_right + 1; col++) tmp_wall_min = min(tmp_wall_min, map[sea_top - 1][col]);
                        for (int col = sea_left - 1; col <= sea_right + 1; col++) tmp_wall_min = min(tmp_wall_min, map[sea_bottom + 1][col]);
                        for (int row = sea_top - 1; row <= sea_bottom + 1; row++) tmp_wall_min = min(tmp_wall_min, map[row][sea_left - 1]);
                        for (int row = sea_top - 1; row <= sea_bottom + 1; row++) tmp_wall_min = min(tmp_wall_min, map[row][sea_right + 1]);

                        if (tmp_sea_max >= tmp_wall_min) continue;

                        tmp = 0;
                        for (int row = sea_top; row <= sea_bottom; row++) {
                            for (int col = sea_left; col <= sea_right; col++) {
                                tmp += tmp_wall_min - map[row][col];
                            }
                        }

                        maximum = max(maximum, tmp);
                    }
                }
            }
        }

        printf("%d\n", maximum);
    }

    return 0;
}

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

using namespace std;

const int INF = 1 << 30;

int main()
{
  int H, W, D[10][10];

  while(cin >> H >> W, H) {
    for(int i = 0; i < H; i++) {
      for(int j = 0; j < W; j++) {
        cin >> D[i][j];
      }
    }
    int ret = 0;
    for(int i = 0; i < H; i++) {
      for(int j = 0; j < W; j++) {
        for(int k = i + 2; k < H; k++) {
          for(int l = j + 2; l < W; l++) {
            int low = 114514, high = -114514, beet = 0;
            for(int m = i; m <= k; m++) low = min(low, D[m][j]);
            for(int m = i; m <= k; m++) low = min(low, D[m][l]);
            for(int m = j; m <= l; m++) low = min(low, D[i][m]);
            for(int m = j; m <= l; m++) low = min(low, D[k][m]);
            for(int m = i + 1; m < k; m++) {
              for(int n = j + 1; n < l; n++) {
                high = max(high, D[m][n]);
                beet += low - D[m][n];
              }
            }
            if(low <= high) continue;
            ret = max(ret, beet);
          }
        }
      }
    }
    cout << ret << endl;
  }
}