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, input().split())
c = []
for _ in range(H):
    *w, = map(int, input().split())
    c.append(w)

# 上方向に連続するタイルの数を記録する
t = []
for _ in range(H+2):
    t.append([0]*(W+2))

for w in range(1, W+1):
    for h in range(1, H+1):
        if c[h-1][w-1] == 1:
            t[h][w] = 0
        else:
            t[h][w] = t[h-1][w]+1

ans = 0
for h in range(1, H+1):
    s = []
    for w in range(1, W+2):
        if len(s) == 0 or s[-1][0] < t[h][w]:
            s.append([t[h][w], w])
        elif s[-1][0] > t[h][w]:
            li = w
            while len(s) > 0 and s[-1][0] >= t[h][w]:
                r = s.pop(-1)
                tmp = (w-r[1])*r[0]
                if tmp > ans:
                    ans = tmp
                li = r[1]
            s.append([t[h][w], li])
print(ans)

