#include <iostream>
#include <algorithm>
#include <vector>
#include <fstream>

using namespace std;

int is_prime(int n){
    for(int d = 2; d*d <= n; ++d)
        if(!(n%d))
            return 0;
    return 1;
}

int main() {
    int n;
    //freopen("input.txt", "r", stdin);
    cin >> n;
    if(n == 4){
        cout << 2;
        return 0;
    }
    if(is_prime(n)){
        cout << n-1;
        return 0;
    }
    cout << 0;
    return 0;
}