A.cpp

#include <bits/stdc++.h>
#define vi vector<int>
#define ma map<int, int>
#define uma unordered_map<int, int>
#define ll long long int
#define pb push_back
#define mod 1000000007
#define int long long
#define loop(i, x, n) for (int i = x; i < n; i++)
#define rloop(i, n) for (int i = n - 1; i >= 0; i--)
#define test  \
    int t;    \
    cin >> t; \
    while (t--)
#define mp make_pair
#define pr pair<int, int>
using namespace std;
/*************************************************************************************************/

void solve()
{
    int n, x, y;
    cin >> n;
    int ans = 0;
    for (int i = 1; i <= n; i++)
    {
        x = i;
        y = n - x;
        if (x > 0 && y > 0)
        {
            ans++;
            // if (x != y)
            //     ans++;
        }
    }
    cout << ans;
}
signed main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    //test
    solve();

    return 0;
}