#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
typedef long long LL;
int n;

int main()
{
    cin>>n;
    int ans = 0;
    double mid = n * 1.0 / 2;
    for (int i = 1; i < n; i ++ )
    {
        if((i*i)%n < mid)
        {
            ans++;
            //cout<<i<<endl;
        }
    }
    cout<<ans<<endl;
    return 0;
}