#include <bits/stdc++.h>
using namespace std;
using LL = long long;
using ULL = unsigned long long;
long long MOD = 1000000000 + 7;
constexpr long long INF = numeric_limits<LL>::max() / 2;
const double PI = acos(-1);
struct Tll {
  LL first, second, third;
};
struct Fll {
  LL first, second, third, fourd;
};
void YN(bool f) {
  if (f)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
}
void yn(bool f) {
  if (f)
    cout << "Yes" << endl;
  else
    cout << "No" << endl;
}
struct Edge {
  LL to, cost;
};
struct edge {
  LL from, to, cost;
};
vector<vector<LL>> g, rev;
vector<edge> edges;
vector<LL> v;
map<LL, LL> ma;
set<LL> st;
LL h, w, n, m, k, t, s, p, q, last, cnt, sum, ans, a[3][3], b[510000],
    dp[50000];
string str, ss;
bool f;
int main() {
  cin >> n;
  cout << n / 2 << endl;
  return 0;
}
