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 = []  # (height, pos) 高さと位置が格納される
    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())
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)
