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
h, w = map(int, raw_input().split())
c = [map(int, raw_input().split()) for i in xrange(h)]
cnt = [[0]*w for i in xrange(h)]

for j in xrange(w):
    seq = 0
    for i in xrange(h):
        if c[i][j] == 0:
            seq += 1
        else:
            seq = 0
        cnt[i][j] = seq
ans = 0
st = [(0, -1)]
for i in xrange(h):
    for j in xrange(w):
        v = cnt[i][j]
        last = j
        while v < st[-1][0]:
            l, k = st.pop()
            last = k
            ans = max(ans, l*(j-k))
        if st[-1][0] < v:
            st.append((v, last))
    while 0 < st[-1][0]:
        l, k = st.pop()
        ans = max(ans, l*(w-k))
print ans