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
# -*- coding: utf-8 -*-
from itertools import product

def rectangle_in_histgram(H):

    def calc(i, h):
        tmp_max = 0
        while stack[-1][1] > h:
            pi, ph = stack.pop()
            tmp_max = max(tmp_max, (i-pi)*ph)
            if len(stack) == 0:
                break

        if len(stack) == 0:
            stack.append([pi, h])
        elif stack[-1][1] < h:
            stack.append([pi, h])
        return tmp_max
    
    stack = [] # loc, height
    S_max = 0
    
    for i, h in enumerate(H):
        if len(stack) == 0:
            stack.append([i, h])
        elif h > stack[-1][1]:
            stack.append([i, h])
        elif h == stack[-1][1]:
            pass
        else:
            tmp_max = calc(i, h)
            S_max = max(S_max, tmp_max)

    tmp_max = calc(i+1, 0)
    S_max = max(S_max, tmp_max)
    return S_max


H, W = tuple(map(int, input().split()))
C = [tuple(map(int, input().split())) for _ in range(H)]
A = [[1]*W for _ in range(H)]
for h, w in product(range(H), range(W)):
    if C[h][w] == 1:
        A[h][w] = 0

for h, w in product(range(1, H), range(W)):
    if C[h][w] == 0:
        A[h][w] = A[h-1][w] + 1

result = 0
for a in A:
    result = max(result, rectangle_in_histgram(a))

print(result)