#include <iostream>
using namespace std;
typedef long long ll;

ll solve(ll N){
  for(ll d=3;d*d<=N;d++){
    if(N % d == 0){
      return d;
    }
  }
  return N;
}

int main(){
  ll N;
  cin >> N;
  cout << solve(N) << endl;
  return 0;
}