#include<iostream>
using namespace std;
int main(){
    int n;
    cin>>n;
    if (n<=0)cout<<"Invalid input";
    else if(n<-1000000 || n>1000000)cout<<"No prime factors found";
    else{
        int p=-1;
        while(n%2==0){p=2;n/2;
    }
    for(int i=3;i*i<=n;i=2)while(n%i==0){p=i;n/i;
    }
    if(n>2)p=n;
    cout<<(p==-1?"No prime factors found":to_string(p));
    }
}