import java.math.BigInteger;


/*

The prime factors of 13195 are 5, 7, 13 and 29.

What is the largest prime factor of the number 600851475143 ?

 */


public class Problem3 {


long solve(long x) {

long i;

for(i = 2; i <= x; i++) {

if(x % i == 0) {

break;

}

}

return x == i? x: solve(x / i);

}

public static void main(String[] args) {

// the largest prime factor of 600851475143 = 6857;

System.out.println(new Problem3().solve(Long.valueOf("600851475143")));

}

}