// editor4
#include<iostream>
#include<cmath>
using namespace std;
int main()
{
    long long n;
    cin>>n;
    if(n<=0)
    {
        cout<<"Invalid input"<<endl;
        return 0;
    }
    if(n==1||n<-10000||n>10000)
    {
        cout<<"No prime factor found"<<endl;
        return 0;
    }
    long long l=-1;
    while(n%2==0)
    {
        l=2;
        n=n/2;
    }
    for(long long i=3;i<=sqrt(n);i+2)
    {
        while(n%i==0)
        {
            l=i;
            n=n/i;
        }
    }
    if(n>2)
    {
        l=n;
    }
    cout<<l<<endl;
    return 0;
}