# Problem 3
"""
The prime factors of 13195 are 5, 7, 13 and 29.

What is the largest prime factor of the number 600851475143 ?

"""
#factorcheck
num = 600851475143
factors = [i for i in range(2,num + 1) if num % i == 0]

#primecheck
prime = []
factors.sort(reverse = True)
for i in factors:
   for u in range(2,i):
       if i % u != 0:
           if u == (i // 2)+1:
               prime.append(i)
               break
           continue
       elif i % u == 0:
           break

print(prime[0])