#include <iostream>
#include <algorithm>
#define NMAX 32000

using namespace std;

bool prim(int x)
{
    int v = min(NMAX, x);
    for(int i = 2; i < v; i++)
        if(x % i == 0)
            return false;
    return true;
}

int main()
{
    int n;
    cin >> n;
    if(n == 4) cout << 2;
    else if(prim(n)) cout << n - 1;
    else cout << 0;
    return 0;
}