# @author: Andrew Johnson
#
# The prime factors of 13195 are 5, 7, 13 and 29.
# What is the largest prime factor of the number 600851475143?

num = 600851475143
i = 2
while (i * i < num):
    while (num % i == 0):
        num = num / i
    i = i + 1

print("%d" % num)