#include<iostream>
using namespace std;
bool isprime(int n)
{
    if(n<1)return false;
    for(int i=2;i*i<=n;i++)
    {
        if(n%i==0)return false;
        return 0;
    }
     
}
int main()
{
    int n;
    cin>>n;
    if(n<=0)
    {
        cout<<"Invalid input";
        return 0;
    }
    int largestPrimeFactor=-1;
    for(int i=2;i<=n;i++)
    {
        if(n%i==0&& isprime(i))
        {
            largestPrimeFactor=i;
        }
    }
    if(largestPrimeFactor==-1)
    {
        cout<<"No prime factor found";
    }
    else{
        cout<<largestPrimeFactor;
    }
    return 0;
}