백준 [ALGORITHM] - 학생 번호 (1235)

def solver(id):
    k = 1
    while True:
        find_k = set()
        for i in id:
            find_k.add(i[-k:])
        if len(find_k) == len(id):
            return k
        k += 1

n = int(input())
id = [input() for _ in range(n)]
print(solver(id))