N = int(input("请输入正整数: "))

if N <= 1:
    print(f"{N}不是质数")
elif N == 2:
    print(f"{N}是质数")
elif N % 2 == 0 or N % 3 == 0:
    print(f"{N}不是质数")
else:
    for i in range(2, N):
        if N % i == 0:
            print(f"{N}不是质数")
            break
    else:
        print(f"{N}是质数")