#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 true;
}
int main(){
    int n;
    cin>>n;
    if(n<=0){
        cout<<"Invalid input";
        return 0;
    }
    int largestPrimeFactors=-1;
    for(int i=2;i<=n;i++){
        if(n % i==0&& isprime(i))
        largestPrimeFactors=i;
}
if(largestPrimeFactor==-1)
cout<<"no prime factors found";
else
cout<<largestPrimeFactors;
return 0;
}