Problem p02865 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;
#define IOS                                                                    \
  ios::sync_with_stdio(0);                                                     \
  cin.tie(0);                                                                  \
  cout.tie(0);
#define endl "\n"
#define int long long
#define all(v) v.begin(), v.end()
#define rep(i, a, b) for (int i = a; i <= b; i++)
#define rep2(i, a, b) for (int i = a; i >= b; i--)
#define f first
#define s second
#define PB push_back
#define MP make_pair
#define db long double
#define trace1(x) cerr << #x << ": " << x << endl
#define trace2(x, y) cerr << #x << ": " << x << " | " << #y << ": " << y << endl
#define trace3(x, y, z)                                                        \
  cerr << #x << ":" << x << " | " << #y << ": " << y << " | " << #z << ": "    \
       << z << endl
#define trace4(a, b, c, d)                                                     \
  cerr << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": "   \
       << c << " | " << #d << ": " << d << endl
#define trace5(a, b, c, d, e)                                                  \
  cerr << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": "   \
       << c << " | " << #d << ": " << d << " | " << #e << ": " << e << endl
#define trace6(a, b, c, d, e, f)                                               \
  cerr << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": "   \
       << c << " | " << #d << ": " << d << " | " << #e << ": " << e << " | "   \
       << #f << ": " << f << endl
#define cases                                                                  \
  int testcases;                                                               \
  cin >> testcases;                                                            \
  while (testcases--)

// void time() {
//     #ifndef ONLINE_JUDGE
//     cout << "\nTime: " << 1.0 * clock() / CLOCKS_PER_SEC << "s\n";
//     #endif
// }

int32_t main() {
#ifndef ONLINE_JUDGE
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
#endif

  IOS

      int n;
  cin >> n;
  cout << (n - 1) / 2;

  // time();
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;
#define IOS                                                                    \
  ios::sync_with_stdio(0);                                                     \
  cin.tie(0);                                                                  \
  cout.tie(0);
#define endl "\n"
#define int long long
#define all(v) v.begin(), v.end()
#define rep(i, a, b) for (int i = a; i <= b; i++)
#define rep2(i, a, b) for (int i = a; i >= b; i--)
#define f first
#define s second
#define PB push_back
#define MP make_pair
#define db long double
#define trace1(x) cerr << #x << ": " << x << endl
#define trace2(x, y) cerr << #x << ": " << x << " | " << #y << ": " << y << endl
#define trace3(x, y, z)                                                        \
  cerr << #x << ":" << x << " | " << #y << ": " << y << " | " << #z << ": "    \
       << z << endl
#define trace4(a, b, c, d)                                                     \
  cerr << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": "   \
       << c << " | " << #d << ": " << d << endl
#define trace5(a, b, c, d, e)                                                  \
  cerr << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": "   \
       << c << " | " << #d << ": " << d << " | " << #e << ": " << e << endl
#define trace6(a, b, c, d, e, f)                                               \
  cerr << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": "   \
       << c << " | " << #d << ": " << d << " | " << #e << ": " << e << " | "   \
       << #f << ": " << f << endl
#define cases                                                                  \
  int testcases;                                                               \
  cin >> testcases;                                                            \
  while (testcases--)

// void time() {
//     #ifndef ONLINE_JUDGE
//     cout << "\nTime: " << 1.0 * clock() / CLOCKS_PER_SEC << "s\n";
//     #endif
// }

int32_t main() {

  IOS

      int n;
  cin >> n;
  cout << (n - 1) / 2;

  // time();
  return 0;
}