#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;
}
itn main(){
    int n;
    cin>>n;
    if(n<0)
    
    {
        cout<<"Invalid input"<<endl;
        return 0;
    }
    int largest =-1;
    for(int i=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;
}