n = int(input())
L = [input() for i in range(n)]
k = len(L[0])
check = False
for i in range(k,-1,-1):
S = set()
for j in range(n):
S.add(L[j][i:k+1])
if len(S) == n:
print(k-i)
check = True
break
if check:
break