#include <bits/stdc++.h>
using namespace std;
template <class T>
inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
using Graph = vector<vector<long long>>;
struct edge {
  long long from, to, cost;
};
signed main() {
  long long a;
  cin >> a;
  cout << a / 2;
}
