Untitled

import math

n = 600851475143

while n % 2 == 0:
    prime = 2

    n //= 2

for i in range(3, int(math.sqrt(n)) + 1, 2):
    while n % i == 0:
        prime = i
        n = n / i

if n > 2:
        prime = n

print(prime)