A Garden with Ponds

Mr. Gardiner is a modern garden designer who is excellent at utilizing the terrain features. His design method is unique: he first decides the location of ponds and design them with the terrain features intact.

According to his unique design procedure, all of his ponds are rectangular with simple aspect ratios. First, Mr. Gardiner draws a regular grid on the map of the garden site so that the land is divided into cells of unit square, and annotates every cell with its elevation. In his design method, a pond occupies a rectangular area consisting of a number of cells. Each of its outermost cells has to be higher than all of its inner cells. For instance, in the following grid map, in which numbers are elevations of cells, a pond can occupy the shaded area, where the outermost cells are shaded darker and the inner cells are shaded lighter. You can easily see that the elevations of the outermost cells are at least three and those of the inner ones are at most two.

<image>

A rectangular area on which a pond is built must have at least one inner cell. Therefore, both its width and depth are at least three.

When you pour water at an inner cell of a pond, the water can be kept in the pond until its level reaches that of the lowest outermost cells. If you continue pouring, the water inevitably spills over. Mr. Gardiner considers the larger capacity the pond has, the better it is. Here, the capacity of a pond is the maximum amount of water it can keep. For instance, when a pond is built on the shaded area in the above map, its capacity is (3 − 1) + (3 − 0) + (3 − 2) = 6, where 3 is the lowest elevation of the outermost cells and 1, 0, 2 are the elevations of the inner cells. Your mission is to write a computer program that, given a grid map describing the elevation of each unit square cell, calculates the largest possible capacity of a pond built in the site.

Note that neither of the following rectangular areas can be a pond. In the left one, the cell at the bottom right corner is not higher than the inner cell. In the right one, the central cell is as high as the outermost cells.

<image>

Input

The input consists of at most 100 datasets, each in the following format.


d w
e1, 1 ... e1, w
...
ed, 1 ... ed, w


The first line contains d and w, representing the depth and the width, respectively, of the garden site described in the map. They are positive integers between 3 and 10, inclusive. Each of the following d lines contains w integers between 0 and 9, inclusive, separated by a space. The x-th integer in the y-th line of the d lines is the elevation of the unit square cell with coordinates (x, y).

The end of the input is indicated by a line containing two zeros separated by a space.

Output

For each dataset, output a single line containing the largest possible capacity of a pond that can be built in the garden site described in the dataset. If no ponds can be built, output a single line containing a zero.

Sample Input


3 3
2 3 2
2 1 2
2 3 1
3 5
3 3 4 3 3
3 1 0 2 3
3 3 4 3 2
7 7
1 1 1 1 1 0 0
1 0 0 0 1 0 0
1 0 1 1 1 1 1
1 0 1 0 1 0 1
1 1 1 1 1 0 1
0 0 1 0 0 0 1
0 0 1 1 1 1 1
6 6
1 1 1 1 2 2
1 0 0 2 0 2
1 0 0 2 0 2
3 3 3 9 9 9
3 0 0 9 0 9
3 3 3 9 9 9
0 0


Output for the Sample Input


0
3
1
9






Example

Input

3 3
2 3 2
2 1 2
2 3 1
3 5
3 3 4 3 3
3 1 0 2 3
3 3 4 3 2
7 7
1 1 1 1 1 0 0
1 0 0 0 1 0 0
1 0 1 1 1 1 1
1 0 1 0 1 0 1
1 1 1 1 1 0 1
0 0 1 0 0 0 1
0 0 1 1 1 1 1
6 6
1 1 1 1 2 2
1 0 0 2 0 2
1 0 0 2 0 2
3 3 3 9 9 9
3 0 0 9 0 9
3 3 3 9 9 9
0 0


Output

0
3
1
9

Source: aizu | Difficulty: UNKNOWN_DIFFICULTY


Solutions:
while True:
	(d, w) = map(int, input().split())
	if d == 0:
		break
	mp = [list(map(int, input().split())) for _ in range(d)]

	def solve():
		ans = 0
		for left in range(w - 1):
			for right in range(w - 1, left + 1, -1):
				for top in range(d - 1):
					for under in range(d - 1, top + 1, -1):
						frame_height = 10
						frame_height = min(frame_height, min(mp[top][left:right + 1]))
						frame_height = min(frame_height, min(mp[under][left:right + 1]))
						frame_height = min(frame_height, min((mp[i][left] for i in range(top, under))))
						frame_height = min(frame_height, min((mp[i][right] for i in range(top, under))))
						pond_height = 0
						pond_height = max(pond_height, max((max(mp[i][left + 1:right]) for i in range(top + 1, under))))
						if pond_height < frame_height:
							temp = frame_height * (under - top - 1) * (right - left - 1) - sum((sum(mp[i][left + 1:right]) for i in range(top + 1, under)))
							ans = max(temp, ans)
		print(ans)
	solve()


while True:
	(d, w) = map(int, input().split())
	if d == 0 and w == 0:
		break
	e = [list(map(int, input().split())) for i in range(d)]
	V = 0
	for i_l in range(d - 2):
		for i_r in range(min(i_l + 2, d), d):
			for j_l in range(w - 2):
				for j_r in range(min(j_l + 2, w), w):
					min_out = 10 ** 10
					max_in = 0
					tmp = 0
					for i in range(i_l, i_r + 1):
						for j in range(j_l, j_r + 1):
							if i == i_l or i == i_r or j == j_l or (j == j_r):
								min_out = min(min_out, e[i][j])
							else:
								max_in = max(max_in, e[i][j])
					for i in range(i_l, i_r + 1):
						for j in range(j_l, j_r + 1):
							if min_out > max_in:
								if i == i_l or i == i_r or j == j_r or (j == j_l):
									1
								else:
									tmp += min_out - e[i][j]
					V = max(tmp, V)
	print(V)


def main():
	while True:
		(d, w) = map(int, input().split())
		if d == 0:
			break
		garden = []
		for i in range(d):
			garden.append(list(map(int, input().split())))
		pondmax = 0
		for tly in range(len(garden)):
			for tlx in range(len(garden[0])):
				for bry in range(tly + 2, len(garden)):
					for brx in range(tlx + 2, len(garden[0])):
						l_gray = []
						d_gray = []
						for spy in range(tly, bry + 1):
							for spx in range(tlx, brx + 1):
								if spy == tly or spy == bry or spx == tlx or (spx == brx):
									d_gray.append(garden[spy][spx])
								else:
									l_gray.append(garden[spy][spx])
						if min(d_gray) > max(l_gray):
							pond = 0
							for depth in l_gray:
								pond += min(d_gray) - depth
							if pond > pondmax:
								pondmax = pond
		print(pondmax)
main()


while True:
	(d, w) = map(int, input().split())
	if d == 0:
		break
	area = []
	for _ in range(d):
		area.append(list(map(int, input().split())))
	a = 0
	for dp in range(1, d - 1):
		for wp in range(1, w - 1):
			for i in range(1, d - dp):
				for j in range(1, w - wp):
					mawari = min(area[i - 1][j - 1:j + wp + 1] + area[i + dp][j - 1:j + wp + 1])
					naka = 0
					for ii in range(dp):
						mawari = min(mawari, area[i + ii][j - 1], area[i + ii][j + wp])
						naka = max([naka] + area[i + ii][j:j + wp])
					if mawari > naka:
						vn = 0
						for ii in range(dp):
							for jj in range(wp):
								vn += mawari - area[i + ii][j + jj]
						a = max(vn, a)
	print(a)


while 1:
	(D, W) = list(map(int, input().split()))
	if (D, W) == (0, 0):
		break
	garden = [list(map(int, input().split())) for _ in range(D)]
	ans = 0
	for wi in range(W):
		for wj in range(wi + 2, W):
			for di in range(D):
				for dj in range(di + 2, D):
					edge_min = float('inf')
					water_sum = 0
					count = 0
					in_max = 0
					for w in range(wi, wj + 1):
						for d in range(di, dj + 1):
							if w in (wi, wj) or d in (di, dj):
								edge_min = min(garden[d][w], edge_min)
							else:
								water_sum += garden[d][w]
								in_max = max(in_max, garden[d][w])
								count += 1
					if edge_min > in_max:
						ans = max(ans, edge_min * count - water_sum)
	print(ans)


import math, string, itertools, fractions, heapq, collections, re, array, bisect, sys, random, time, copy, functools
sys.setrecursionlimit(10 ** 7)
inf = 10 ** 20
eps = 1.0 / 10 ** 13
mod = 10 ** 9 + 7
dd = [(-1, 0), (0, 1), (1, 0), (0, -1)]
ddn = [(-1, 0), (-1, 1), (0, 1), (1, 1), (1, 0), (1, -1), (0, -1), (-1, -1)]

def LI():
	return [int(x) for x in sys.stdin.readline().split()]

def LI_():
	return [int(x) - 1 for x in sys.stdin.readline().split()]

def LF():
	return [float(x) for x in sys.stdin.readline().split()]

def LS():
	return sys.stdin.readline().split()

def I():
	return int(sys.stdin.readline())

def F():
	return float(sys.stdin.readline())

def S():
	return input()

def pf(s):
	return print(s, flush=True)

def main():
	rr = []

	def f(d, w):
		aa = [LI() for _ in range(d)]
		r = 0
		for i in range(d - 2):
			for j in range(w - 2):
				for k in range(i + 2, d):
					for l in range(j + 2, w):
						mi = inf
						for m in range(i, k + 1):
							t = aa[m][j]
							if mi > t:
								mi = t
							t = aa[m][l]
							if mi > t:
								mi = t
						for m in range(j, l + 1):
							t = aa[i][m]
							if mi > t:
								mi = t
							t = aa[k][m]
							if mi > t:
								mi = t
						s = 0
						for m in range(i + 1, k):
							for n in range(j + 1, l):
								if mi <= aa[m][n]:
									s = -inf
									break
								s += mi - aa[m][n]
						if r < s:
							r = s
		return r
	while 1:
		(n, m) = LI()
		if n == 0:
			break
		rr.append(f(n, m))
	return '\n'.join(map(str, rr))
print(main())


import sys
sys.setrecursionlimit(10 ** 9)
input = sys.stdin.readline

def calcVolume(L, R, T, B, min_wall):
	ret = 0
	for w in range(L, R + 1):
		for h in range(B, T + 1):
			ret += min_wall - garden[h][w]
	return ret

def pondsVolume(L, R, T, B):
	max_in_pond = 0
	for w in range(L, R + 1):
		for h in range(B, T + 1):
			max_in_pond = max(max_in_pond, garden[h][w])
	min_wall = float('inf')
	for w in range(L - 1, R + 2):
		min_wall = min(min_wall, garden[B - 1][w], garden[T + 1][w])
	for h in range(B - 1, T + 2):
		min_wall = min(min_wall, garden[h][L - 1], garden[h][R + 1])
	if min_wall <= max_in_pond:
		return -1
	else:
		return calcVolume(L, R, T, B, min_wall)
while True:
	(d, w) = map(int, input().split())
	if d == 0:
		break
	garden = [list(map(int, input().split())) for _ in range(d)]
	ans = 0
	wallMin = 0
	for L in range(1, w - 1):
		for B in range(1, d - 1):
			for R in range(L, w - 1):
				for T in range(B, d - 1):
					ans = max(ans, pondsVolume(L, R, T, B))
	print(ans)


import sys
from itertools import permutations, combinations, product

def input():
	return sys.stdin.readline().strip()

def INT():
	return int(input())

def LIST():
	return list(map(int, input().split()))

def MAP():
	return map(int, input().split())
ans = []
while 1:
	(d, w) = MAP()
	if d == 0 and w == 0:
		break
	e = [LIST() for _ in range(d)]
	sum_max = 0
	for i in combinations(range(d), 2):
		if abs(i[0] - i[1]) == 1:
			continue
		for j in combinations(range(w), 2):
			if abs(j[0] - j[1]) == 1:
				continue
			min_ = 10
			for k in range(i[0], i[1] + 1):
				if k == i[0] or k == i[1]:
					for l in range(j[0], j[1] + 1):
						min_ = min(min_, e[k][l])
				else:
					min_ = min(min_, e[k][j[0]])
					min_ = min(min_, e[k][j[1]])
			sum_ = 0
			for k in range(i[0] + 1, i[1]):
				for l in range(j[0] + 1, j[1]):
					if e[k][l] >= min_:
						sum_ = 0
						break
					else:
						sum_ += min_ - e[k][l]
				if e[k][l] >= min_:
					break
			sum_max = max(sum_max, sum_)
	ans.append(sum_max)
for x in ans:
	print(x)


while 1:
	(d, w) = map(int, input().split())
	if d == w == 0:
		break
	E = [list(map(int, input().split())) for i in range(d)]
	ans = 0
	for x2 in range(d):
		for y2 in range(w):
			for x1 in range(x2 - 1):
				for y1 in range(y2 - 1):
					co = 10 ** 18
					for x in range(x1, x2 + 1):
						co = min(co, E[x][y1], E[x][y2])
					for y in range(y1, y2 + 1):
						co = min(co, E[x1][y], E[x2][y])
					ci = cnt = 0
					for x in range(x1 + 1, x2):
						for y in range(y1 + 1, y2):
							ci = max(ci, E[x][y])
							cnt += E[x][y]
					if ci < co:
						ans = max(ans, (x2 - x1 - 1) * (y2 - y1 - 1) * co - cnt)
	print(ans)


def f(l, r, u, d):
	global e, no
	res = 0
	hori = 10
	for i in range(u, d + 1):
		if i == u or i == d:
			hori = min(hori, min(e[i][l:r + 1]))
		else:
			hori = min(hori, e[i][l], e[i][r])
	if hori == no:
		return 0
	for i in range(u + 1, d):
		for j in range(l + 1, r):
			if hori <= e[i][j]:
				return 0
			res += abs(hori - e[i][j])
	return res
while True:
	(D, W) = map(int, input().split())
	if D + W == 0:
		break
	e = [list(map(int, input().split())) for _ in range(D)]
	for i in range(D):
		no = min(e[0]) if i == 0 else min(no, min(e[i]))
	ans = 0
	for l in range(W - 2):
		for r in range(l + 2, W):
			for u in range(D - 2):
				for d in range(u + 2, D):
					ans = max(ans, f(l, r, u, d))
	print(ans)


while 1:
	(d, w) = map(int, input().split())
	if d == w == 0:
		break
	E = [0] * d
	for i in range(d):
		(*E[i],) = map(int, input().split())
	ans = 0
	for x2 in range(d):
		for y2 in range(w):
			for x1 in range(x2 - 1):
				for y1 in range(y2 - 1):
					co = 10 ** 18
					for x in range(x1, x2 + 1):
						co = min(co, E[x][y1], E[x][y2])
					for y in range(y1, y2 + 1):
						co = min(co, E[x1][y], E[x2][y])
					ci = cnt = 0
					for x in range(x1 + 1, x2):
						for y in range(y1 + 1, y2):
							ci = max(ci, E[x][y])
							cnt += E[x][y]
					if ci < co:
						ans = max(ans, (x2 - x1 - 1) * (y2 - y1 - 1) * co - cnt)
	print(ans)


while True:
	(n, m) = map(int, input().split())
	if n == 0 and m == 0:
		break
	E = [list(map(int, input().split())) for i in range(n)]
	ans = 0
	for x in range(n - 2):
		for y in range(m - 2):
			for w in range(3, n - x + 1):
				for h in range(3, m - y + 1):
					N = 0
					A = E[x][y]
					B = 0
					for i in range(w):
						for j in range(h):
							if i == 0 or j == 0 or j == h - 1 or (i == w - 1):
								A = min(A, E[x + i][y + j])
							else:
								B = max(B, E[x + i][y + j])
					if A > B:
						for i in range(w):
							for j in range(h):
								if i != 0 and j != 0 and (j != h - 1) and (i != w - 1):
									N = N + A - E[x + i][y + j]
					ans = max(ans, N)
	print(ans)


def solve(d, w, f):
	ans = 0
	for i in range(d - 2):
		for j in range(i + 2, d):
			for k in range(w - 2):
				for l in range(k + 2, w):
					minOut = 10
					for m in range(i, j + 1):
						if minOut > f[m][k]:
							minOut = f[m][k]
						if minOut > f[m][l]:
							minOut = f[m][l]
					for m in range(k, l + 1):
						if minOut > f[i][m]:
							minOut = f[i][m]
						if minOut > f[j][m]:
							minOut = f[j][m]
					total = 0
					for m in range(i + 1, j):
						for n in range(k + 1, l):
							total += minOut - f[m][n]
							if minOut <= f[m][n]:
								total -= 10 ** 5
					if ans < total:
						ans = total
	return ans
while True:
	(d, w) = [int(i) for i in input().split()]
	if d == 0:
		break
	f = []
	for i in range(d):
		f.append([int(i) for i in input().split()])
	print(solve(d, w, f))


while True:
	(d, w) = map(int, input().split())
	if d + w == 0:
		break
	pond = [list(map(int, input().split())) for _ in range(d)]
	ans = 0
	for left in range(w - 1):
		for right in range(w - 1, left + 1, -1):
			for top in range(d - 1):
				for under in range(d - 1, top + 1, -1):
					outh = 10
					outh = min(outh, min(pond[top][left:right + 1]))
					outh = min(outh, min(pond[under][left:right + 1]))
					zpond = list(zip(*pond))
					outh = min(outh, min(zpond[left][top:under]))
					outh = min(outh, min(zpond[right][top:under]))
					pondh = 0
					for i in range(top + 1, under):
						pondh = max(pondh, max(pond[i][left + 1:right]))
					if pondh < outh:
						cap = outh * (under - top - 1) * (right - left - 1) - sum((sum(pond[i][left + 1:right]) for i in range(top + 1, under)))
						ans = max(cap, ans)
	print(ans)


import itertools

def rdp_connect() -> bool:
	global h, w, e
	(h, w) = map(int, input().split())
	if h == 0 and w == 0:
		return False
	e = [list(map(int, input().split())) for _ in range(h)]
	return True

def rdp_scan(x1: int, y1: int, x2: int, y2: int) -> int:
	edges = []
	edges.extend([e[j][x1] for j in range(y1, y2 + 1)])
	edges.extend([e[j][x2] for j in range(y1, y2 + 1)])
	edges.extend([e[y1][i] for i in range(x1 + 1, x2)])
	edges.extend([e[y2][i] for i in range(x1 + 1, x2)])
	inner = [e[j][i] for (j, i) in itertools.product(range(y1 + 1, y2), range(x1 + 1, x2))]
	edges_min = min(edges)
	if edges_min - max(inner) <= 0:
		return 0
	return sum(map(lambda e: edges_min - e, inner))
while rdp_connect():
	best = 0
	for (y1, x1) in itertools.product(range(h), range(w)):
		for (y2, x2) in itertools.product(range(y1 + 2, h), range(x1 + 2, w)):
			best = max(best, rdp_scan(x1, y1, x2, y2))
	print(best)


while True:
	(d, w) = map(int, input().split())
	if d == 0:
		break
	e = list((list(map(int, input().split())) for i in range(d)))
	ans = 0
	for sx in range(w - 2):
		for sy in range(d - 2):
			for tx in range(sx + 2, w):
				for ty in range(sy + 2, d):
					max_out = float('inf')
					for i in range(sx, tx + 1):
						max_out = min(e[sy][i], e[ty][i], max_out)
					for i in range(sy, ty + 1):
						max_out = min(e[i][sx], e[i][tx], max_out)
					v = 0
					for j in range(sx + 1, tx):
						for i in range(sy + 1, ty):
							v += max_out - e[i][j]
							if max_out - e[i][j] <= 0:
								v = -float('inf')
					ans = max(v, ans)
	print(ans)


from itertools import product
while True:
	(d, w) = map(int, input().split())
	if d == 0:
		exit()
	ans = 0
	e = [list(map(int, input().split())) for _ in range(d)]
	for (si, sj) in product(range(1, d - 1), range(1, w - 1)):
		for (ti, tj) in product(range(si + 1, d), range(sj + 1, w)):
			mx = 0
			for (i, j) in product(range(si, ti), range(sj, tj)):
				mx = max(mx, e[i][j])
			mn = 100
			for (i, j) in product([si - 1, ti], range(sj - 1, tj + 1)):
				mn = min(mn, e[i][j])
			for (i, j) in product(range(si - 1, ti + 1), [sj - 1, tj]):
				mn = min(mn, e[i][j])
			if mx >= mn:
				continue
			tmp = 0
			for (i, j) in product(range(si, ti), range(sj, tj)):
				tmp += mn - e[i][j]
			ans = max(ans, tmp)
	print(ans)


while True:
	(d, w) = map(int, input().split())
	if d == 0:
		break
	area = []
	for _ in range(d):
		area.append(list(map(int, input().split())))
	v = 0
	for dp in range(1, d - 1):
		for wp in range(1, w - 1):
			for i in range(1, d - dp):
				for j in range(1, w - wp):
					mawari = min(area[i - 1][j - 1:j + wp + 1] + area[i + dp][j - 1:j + wp + 1])
					naka = 0
					for ii in range(dp):
						mawari = min(mawari, area[i + ii][j - 1], area[i + ii][j + wp])
						naka = max([naka] + area[i + ii][j:j + wp])
					if mawari > naka:
						vn = 0
						for ii in range(dp):
							for jj in range(wp):
								vn += mawari - area[i + ii][j + jj]
						v = max(vn, v)
	print(v)


while 1:
	(h, w) = map(int, input().split())
	if h == w == 0:
		break
	s = [list(map(int, input().split())) for i in range(h)]
	ans = 0
	for u in range(h):
		for d in range(u + 2, h):
			for l in range(w):
				for r in range(l + 2, w):
					m = float('inf')
					for i in range(u, d + 1):
						m = min(m, s[i][l], s[i][r])
					for i in range(l, r + 1):
						m = min(m, s[u][i], s[d][i])
					f = 1
					su = 0
					for i in range(u + 1, d):
						for j in range(l + 1, r):
							su += m - s[i][j]
							if s[i][j] >= m:
								f = 0
								break
						if not f:
							break
					if f:
						ans = max(ans, su)
	print(ans)


def check(ry, rx, x, y, f):
	tmpmin = float('inf')
	for yi in range(ry):
		tmpmin = min(tmpmin, f[yi + y][x])
	for xi in range(rx):
		tmpmin = min(tmpmin, f[y][xi + x])
	for yi in range(ry):
		tmpmin = min(tmpmin, f[yi + y][x + rx - 1])
	for xi in range(rx):
		tmpmin = min(tmpmin, f[ry - 1 + y][x + xi])
	res = 0
	for yi in range(y + 1, y + ry - 1):
		for xi in range(x + 1, x + rx - 1):
			res += tmpmin - f[yi][xi]
			if f[yi][xi] >= tmpmin:
				return 0
	return res

def main(d, w):
	field = [list(map(int, input().split())) for i in range(d)]
	res = 0
	for ry in range(3, d + 1):
		for rx in range(3, w + 1):
			for y in range(d - ry + 1):
				for x in range(w - rx + 1):
					res = max(res, check(ry, rx, x, y, field))
	print(res)
while 1:
	(d, w) = map(int, input().split())
	if d == w == 0:
		break
	main(d, w)


from itertools import product
while True:
	(d, w) = map(int, input().split())
	if d == 0:
		break
	gridgraph = [list(map(int, input().split())) for _ in range(d)]
	ans = 0
	for (si, sj) in product(range(1, d - 1), range(1, w - 1)):
		for (ti, tj) in product(range(si, d - 1), range(sj, w - 1)):
			max_in_area = 0
			for (i, j) in product(range(si, ti + 1), range(sj, tj + 1)):
				max_in_area = max(max_in_area, gridgraph[i][j])
			huti_min = 100
			for (i, j) in product([si - 1, ti + 1], range(sj - 1, tj + 2)):
				huti_min = min(huti_min, gridgraph[i][j])
			for (i, j) in product(range(si - 1, ti + 2), [sj - 1, tj + 1]):
				huti_min = min(huti_min, gridgraph[i][j])
			if max_in_area >= huti_min:
				continue
			tmp = 0
			for (i, j) in product(range(si, ti + 1), range(sj, tj + 1)):
				tmp += huti_min - gridgraph[i][j]
			ans = max(ans, tmp)
	print(ans)


import sys
import re
from collections import deque, defaultdict, Counter
from math import ceil, sqrt, hypot, factorial, pi, sin, cos, radians, log2, gcd
from itertools import permutations, combinations, product
from operator import itemgetter, mul
from copy import deepcopy
from string import ascii_lowercase, ascii_uppercase, digits

def input():
	return sys.stdin.readline().strip()

def INT():
	return int(input())

def MAP():
	return map(int, input().split())

def LIST():
	return list(map(int, input().split()))
sys.setrecursionlimit(10 ** 9)
INF = float('inf')
mod = 10 ** 9 + 7

def main():
	ans = []
	while 1:
		(d, w) = MAP()
		if d == 0 and w == 0:
			break
		else:
			lis = []
			e = [LIST() for _ in range(d)]
			for x in combinations(range(d), 2):
				for y in combinations(range(w), 2):
					if x[1] - x[0] != 1 and y[1] - y[0] != 1:
						waku_min = 9
						naka_max = 0
						a = 0
						for p in range(x[0], x[1] + 1):
							for q in range(y[0], y[1] + 1):
								if p == x[0] or p == x[1] or q == y[0] or (q == y[1]):
									waku_min = min(waku_min, e[p][q])
								else:
									naka_max = max(naka_max, e[p][q])
						if waku_min > naka_max:
							for p in range(x[0] + 1, x[1]):
								for q in range(y[0] + 1, y[1]):
									a += waku_min - e[p][q]
							lis.append(a)
			if not lis:
				ans.append(0)
			else:
				ans.append(max(lis))
	for x in ans:
		print(x)
main()


while True:
	(h, w) = map(int, input().split())
	if h + w == 0:
		break
	e = list((list((int(i) for i in input().split())) for i in range(h)))
	e_T = list(zip(*e))
	ans = 0
	for i in range(h - 2):
		for j in range(w - 2):
			for k in range(i + 2, h):
				for l in range(j + 2, w):
					flag = False
					count = 0
					wall = min(min(e[i][j:l + 1]), min(e[k][j:l + 1]), min(e_T[j][i:k + 1]), min(e_T[l][i:k + 1]))
					for m in range(i + 1, k):
						for n in range(j + 1, l):
							if wall > e[m][n]:
								count += wall - e[m][n]
							else:
								flag = True
								break
						if flag:
							break
					if ans < count and (not flag):
						ans = count
	print(ans)