#include<iostream>
#include<cmath>
using namespace std;

bool isPrime(int num)
{
    if(num<2)return false;
    for(int i=2;i<=sqrt(num);++i)
    if(num%i==0)
    return false;
    return true;
}
int main()
{
    int n;
    cin>>n;
    if(n<=0)
    {
        cout<<"Invalid input"<<endl;
        return 0;
    }
    int largest= -1;
    for(int=2;i<=n;++i)
    {
        if(n%i==0 && isPrime(i))
        largest= i;
    }
    if(largest==-1)
    cout<<"No prime factors found"<<endl;
    else
    cout<<largest<<endl;
    return 0;
}