/* 문제
*/
// 2014.
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <vector>
#include <queue>
#include <functional>
#include <cstring>
#include <string>
#include <map>
using namespace std;
long long Q[2000000];
map <long long, bool> M;
int main()
{
long long n;
scanf("%lld", &n);
Q[0] = 0;
int ans = 0;
for (int i = 1; i <= 2*n; i++)
{
Q[i] = (Q[i - 1] + (long long)i)%n;
// printf("%lld\n", Q[i]);
M[Q[i]] = true;
}
if (n % 2)
{
printf("%lld\n", n / 2);
}
else
printf("%lld\n", n - 1);
return 0;
}
