#include <bits/stdc++.h>
using namespace std;
using ll = long long;
struct edge {
  int to, cost;
};
const int INF = 1e9;
const int MOD = 1e9 + 7;
const double EPS = 1.0e-10;
const double PI = acos(-1.0);
const int mx4[] = {0, 1, 0, -1};
const int my4[] = {1, 0, -1, 0};
const int mx8[] = {0, 1, 1, 1, 0, -1, -1, -1};
const int my8[] = {1, 1, 0, -1, -1, -1, 0, 1};
ll Pow(ll x, ll n) {
  ll res = 1;
  while (n > 0) {
    if (n & 1) res = res * x % MOD;
    x = x * x % MOD;
    n >>= 1;
  }
  return res;
}
int main() {
  int n;
  cin >> n;
  cout << n / 2 << "\n";
  return 0;
}
