Buggy python submission (verdict: Runtime Error):
# -*- coding: utf-8 -*-
"""
http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=0044
?´???°II
"""
import sys


def create_prime_list(limit):
    """ ??¨??????????????????????????§limit?????§????´???°?????????????±???????
    https://ja.wikipedia.org/wiki/%E3%82%A8%E3%83%A9%E3%83%88%E3%82%B9%E3%83%86%E3%83%8D%E3%82%B9%E3%81%AE%E7%AF%A9
    """
    x = limit**0.5
    primes = []
    # print('x={0}'.format(x))
    nums = [x for x in range(2, limit+1)]
    while nums[0] <= x:
        primes.append(nums[0])
        current_prime = nums[0]
        nums = [x for x in nums if x % current_prime != 0]
    primes.extend(nums)
    # print(primes)
    return primes


def main(args):
    primes = create_prime_list(50000)  # ?´???°????????????????????¨???
    
    for line in sys.stdin:  # ??????????????\???
        limit = int(line.strip())
        unders = [x for x in primes if x < limit]
        largest_prime = unders[-1]
        overs = [x for x in primes if x > limit]
        smallest_prime = overs[0]
        
        # ???????????????
        print('{0} {1}'.format(largest_prime, smallest_prime))


if __name__ == '__main__':
    main(sys.argv[1:])

Fixed submission:
# -*- coding: utf-8 -*-
"""
http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=0044
"""

from math import sqrt, ceil, pow
import bisect
import sys


# https://github.com/mccricardo/sieve_of_atkin/blob/master/sieve_of_atkin.py
class SieveOfAtkin:
    def __init__(self, limit):
        self.limit = limit
        self.primes = []
        self.sieve = [False] * (self.limit + 1)

    def flip(self, prime):
        try:
            self.sieve[prime] = True if self.sieve[prime] == False else False
        except KeyError:
            pass

    def invalidate(self, prime):
        try:
            if self.sieve[prime] == True: self.sieve[prime] = False
        except KeyError:
            pass

    def isPrime(self, prime):
        try:
            return self.sieve[prime]
        except KeyError:
            return False

    def getPrimes(self):
        testingLimit = int(ceil(sqrt(self.limit)))

        for i in range(testingLimit):
            for j in range(testingLimit):
                # n = 4*i^2 + j^2
                n = 4 * int(pow(i, 2)) + int(pow(j, 2))
                if n <= self.limit and (n % 12 == 1 or n % 12 == 5):
                    self.flip(n)

                # n = 3*i^2 + j^2
                n = 3 * int(pow(i, 2)) + int(pow(j, 2))
                if n <= self.limit and n % 12 == 7:
                    self.flip(n)

                # n = 3*i^2 - j^2
                n = 3 * int(pow(i, 2)) - int(pow(j, 2))
                if n <= self.limit and i > j and n % 12 == 11:
                    self.flip(n)

        for i in range(5, testingLimit):
            if self.isPrime(i):
                k = int(pow(i, 2))
                for j in range(k, self.limit, k):
                    self.invalidate(j)

        self.primes = [2, 3] + [x for x in range(len(self.sieve)) if self.isPrime(x) and x >= 5]
        return self.primes




def solve1(num, primes):
    #
    i = bisect.bisect_left(primes, num)
    lt = primes[i-1]
    i = bisect.bisect_right(primes, num)
    gt = primes[i]
    return lt, gt


if __name__ == '__main__':
    A = SieveOfAtkin(55000)
    A.getPrimes()
    # ??????????????\?????¨???????????????
    for line in sys.stdin:
        num = int(line)
        lt, gt = solve1(num, A.primes)
        print('{} {}'.format(lt, gt))