#include <iostream>
#include <algorithm>
#include <vector>
#include <cstring>
#include <cmath>

using namespace std;

bool isprime[1000000];

void search(int n)
{
    memset(isprime, true, sizeof(isprime));

    isprime[0] = false;
    isprime[1] = false;

    for(int i = 2; i < sqrt(n); i++)
    {
        if(isprime[i])
        {
            for(int j = 0; i * (j + 2) < n; j++)
            {
                isprime[i * (j + 2)] = false;
            }
        }
    }
}

using ll = long long int;

int main()
{
    ll N; 
    cin >> N;
    search(N);
    ll num = 0ll;
    for(int i = 0; i < sqrt(N); i++)
    {
       if(isprime[i])
       {
           if(N % i == 0)
           {
               num = i;
           }
       }
    }

    cout << num << endl;

    return 0;
}