664 B | 664 chars
import sys
from math import sqrt, pi, sin, factorial, ceil, floor
BLANK = " "
inp = input
# inp = lambda : sys.stdin.readline()[:-1].strip()
mii = lambda x = BLANK : [*map(int,inp().split(x))]
mfi = lambda x = BLANK : [*map(float,inp().split(x))]
ii = lambda : int(inp())
fi = lambda : float(inp())
p = print
def solve():
while 1:
n = ii()
if n == 0:
break
l = [input() for _ in range(n)]
cnt = -1
for _ in range(100):
if "" in l:
break
if len(set(l)) < n:
break
l = [i[1:] for i in l]
cnt += 1
p(cnt)
if __name__ == "__main__":
tc = 1
for t in range(1, tc+1):
ret = solve()