n, m = map(int, input().split())

from collections import *
d = defaultdict(int)

for _ in range(n):
    s = input()
    for i in range(m):
        if s[i] == "x":
            d[i] += 1

ans = 0
for i in range(n):
    ans = max(ans, d[i]+1)

print(ans)