#include<iostream>
#include<iomanip>
#include <stdint.h>
#include <math.h>
using namespace std;



int main() {
	long double Num = 0.0L;
	bool prim = true;
	for(long double i=5.0L; i<(600851475143L)/2; i+=2)
	{
		prim = true;
		for(long double z=3.0L; z<sqrt(i); z+=2)
		{
			if(fmod(i, z) == 0)
			{
				prim = false;
				break;
			}
		}
		if(prim)
			if(fmod(600851475143L, i)==0)
				Num = i;
    }
	cout << Num << "\n";
	system("Pause");
    return 0;
}