from math import sqrt

def is_prime(x):
    """
    Check if `x` is prime.
    """
    return all(x % i != 0 for i in range(2, int(sqrt(x)) + 2))


def next_prime(x):
    """
    Find the next prime number that is strictly bigger than `x`.
    """
    for i in range(x+1, 2 * x):
        if is_prime(i):
            return i