寻找最接近的素数

import math

def is_prime(num):
    if num < 2:
        return False
    for i in range(2, int(math.sqrt(num)) + 1):
        if num % i == 0:
            return False
    return True

def find_closest_prime(num):
    if num < 2:
        return None

    lower = num - 1
    upper = num + 1

    while True:
        if is_prime(lower):
            return lower
        elif is_prime(upper):
            return upper
        else:
            lower -= 1
            upper += 1

# 测试示例
num = 123
closest_prime = find_closest_prime(num)
print("最接近的素数是:", closest_prime)