import sys
input = lambda: sys.stdin.readline().rstrip()
ii = lambda: int(input())
mi = lambda: map(int, input().split())
li = lambda: list(mi())
INF = 2 ** 63 - 1
mod = 998244353

n, m = mi()

s = [input() for _ in range(n)]

ok = n

ng = 0

def check(k):
    for i in range(m):
        cnt = 0
        for j in range(n):
            if s[j][i] == 'x':
                cnt += 1
        if cnt >= k:
            return False
    return True

while abs(ok - ng) > 1:
    mid = (ok + ng) // 2
    if check(mid):
        ok = mid
    else:
        ng = mid
print(ok)