#include <iostream>

using namespace std;

int main()
{
    int n, p=1;
    cin>> n;

    if (n==4)
            cout<< "2";
    else
    {
        for (int i=2; i*i<=n && p==1; i++)
        {
            if (n%i==0)
                p=0;
        }

        if (p==0)
            cout << "0";
        else
            if (p==1)
                cout <<n-1;
    }
    cout<<'\n';

    return 0;
}