#include <bits/stdc++.h>
using namespace std;
long long INF = 1e18;
struct custom_hash {
  static uint64_t splitmix64(uint64_t x) {
    x += 0x9e3779b97f4a7c15;
    x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
    x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
    return x ^ (x >> 31);
  }
  size_t operator()(uint64_t x) const {
    static const uint64_t FIXED_RANDOM =
        chrono::steady_clock::now().time_since_epoch().count();
    return splitmix64(x + FIXED_RANDOM);
  }
};
template <class T>
void read(T arr[], long long n) {
  for (long long i = (0); i < (long long)(n); i++) cin >> arr[i];
}
long long mystoi(string str) {
  stringstream ss(str);
  long long ans = 0;
  ss >> ans;
  return ans;
}
long long exp(long long x, long long ex, long long p) {
  long long ans = 1ll;
  while (ex > 0) {
    if (ex & 1ll) ans = (ans * x) % p;
    ex >>= 1ll;
    x = (x * x) % p;
  }
  return ans;
}
bool sort_cond(const pair<long long, long long> &a,
               const pair<long long, long long> &b) {
  return ((a.first - a.second) > (b.first - b.second));
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long t = 1;
  while (t--) {
    long long n;
    cin >> n;
    cout << n / 2 << endl;
  }
}
