题解 | 小红的合数寻找

def is_prime(n):
    if n <= 1:
        return False
    if n == 2:
        return True
    if n % 2 == 0:
        return False
    for i in range(3, int(n**0.5) + 1, 2):
        if n % i == 0:
            return False
    return True

x = int(input())
found = -1

for num in range(x, 2 * x + 1):
    if num > 1 and not is_prime(num):
        found = num
        break

print(found)