#include <iostream>
using namespace std;

long long findprimefactor(long long StartNumber)
{
    for (long long start=2; start < (StartNumber/2)+1; start++)
    {
        if (StartNumber % start == 0)
        {
                        return findprimefactor(StartNumber/start);
        }
    }
    return StartNumber;
}

int main()
{
    cout << "Enter a number: ";
    long long number;
    cin >> number;
    cout << "the greatest prime factor of " << number << " is " << findprimefactor(number) << endl;
    system("PAUSE");
}