#include <bits/stdc++.h>
#pragma GCC optimize("O3")
#pragma GCC target("sse4")
using namespace std;
using ll = long long;
const int MOD = 1000000007;
const ll INF = 1e18;
const int MX = 100001;
int main() {
  ios_base ::sync_with_stdio(0);
  cin.tie(0);
  int n;
  cin >> n;
  n = n >> 1;
  cout << n;
  return 0;
}
