Given a matrix (H × W) which contains only 1 and 0, find the area of the largest rectangle which only contains 0s.

Constraints

* 1 ≤ H, W ≤ 1,400

Input


H W
c1,1 c1,2 ... c1,W
c2,1 c2,2 ... c2,W
:
cH,1 cH,2 ... cH,W


In the first line, two integers H and W separated by a space character are given. In the following H lines, ci,j, elements of the H × W matrix, are given.

Output

Print the area (the number of 0s) of the largest rectangle.

Example

Input

4 5
0 0 1 0 0
1 0 0 0 0
0 0 0 1 0
0 0 0 1 0


Output

6
def rectangle(n, hs):
  stack = [] #高さと位置を格納
  ans = 0
  for i, h in enumerate(hs):
    j = i
    while stack and stack[-1][0] > h:
      pre_h, j = stack.pop()
      ans = max(ans, (i - j) * pre_h)

    if not stack or stack[-1][0] < h:
      stack.append((h, j))

  ans = max(ans, max((n-j) * h2 for h2, j in stack))

  return ans

H, W = map(int, input().split())

#ここでリストを固定化しておかないと値を受け付けてくれない
hist = [0] * W
result = 0
for _ in range(H):
  ht = list(map(int, input().split()))
  hist = list(map(lambda pre, cur: (pre+1) * (cur ^ 1), hist, ht))
  result = max(result, rectangle(W, hist))
print(result)
