#include <bits/stdc++.h>
using namespace std;

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    long long n;
    cin >> n;

    vector<bool> F(n, true);
    F[0] = F[1] = false;
    for(long long i = 2; i <= (long long)sqrt(n); i++){
        if(F[i]){
            for(long long j = i * 2; j <= n; j += i){
                F[j] = false;
            }
        }
    }

    for(long long i = 3; i <= n; i++){
        if(F[i] and n % i == 0){
            cout << i << endl;
            return 0;
        }
    }


    return 0;
}