import sys
input = sys.stdin.readline
while True:
N,M = map(int,input().split())
if not N+M:
break
arr = [list(map(int,input().split())) for _ in range(N)]
maze = [[0 for _ in range(M)] for _ in range(N)]
for y in range(M):
maze[0][y] = arr[0][y]
for x in range(1,N):
for y in range(M):
if arr[x][y]:
maze[x][y] = maze[x-1][y] + arr[x][y]
result = 0
for x in range(N):
col_idx = 0
stack = []
while col_idx<M:
if stack:
if stack[-1] <= maze[x][col_idx]:
stack.append(maze[x][col_idx])
col_idx += 1
else:
size_stack = len(stack)
min_value = stack[-1]
cu_idx = -1
for i in range(size_stack):
result = max(result,min_value*(i+1))
cu_idx -= 1
if abs(cu_idx)<=size_stack and min_value > stack[cu_idx]:
min_value = stack[cu_idx]
if maze[x][col_idx]:
stack.append(maze[x][col_idx])
else:
stack.clear()
col_idx += 1
else:
if maze[x][col_idx]:
stack.append(maze[x][col_idx])
col_idx += 1
if stack:
size_stack = len(stack)
min_value = stack[-1]
cu_idx = -1
for i in range(size_stack):
result = max(result,min_value*(i+1))
cu_idx -= 1
if abs(cu_idx)<=size_stack and min_value > stack[cu_idx]:
min_value = stack[cu_idx]
print(result)
import sys
input = sys.stdin.readline
while True:
N,M = map(int,input().split())
arr = [[0] + list(map(int,input().split())) + [0] for i in range(N)]
if N+M == 0:
break
for i in range(1,N):
for j in range(1,M+1):
if arr[i][j]:
arr[i][j] = arr[i-1][j] + 1
result = 0
for i in range(N):
stack = [0]
for j in range(1,M+2):
while stack and arr[i][j] < arr[i][stack[-1]]:
height = arr[i][stack[-1]]
stack.pop()
width = j-stack[-1] - 1
result = max(result,height*width)
stack.append(j)
print(result)