#include <bits/stdc++.h>
using namespace std;
template <typename S, typename T>
ostream& operator<<(ostream& out, const pair<S, T> p) {
  out << "(" << p.first << "," << p.second << ")";
  return out;
}
template <typename T>
ostream& operator<<(ostream& out, const vector<T>& v) {
  for (auto a : v) out << a << " ";
  return out;
}
template <typename T>
ostream& operator<<(ostream& out, const set<T>& S) {
  for (auto a : S) cout << a << " ";
  return out;
}
template <typename T>
ostream& operator<<(ostream& out, const multiset<T>& S) {
  for (auto a : S) cout << a << " ";
  return out;
}
template <typename S, typename T>
ostream& operator<<(ostream& out, const map<S, T>& M) {
  for (auto m : M) cout << "(" << m.first << "->" << m.second << ") ";
  return out;
}
template <typename S, typename T>
pair<S, T> operator+(pair<S, T> a, pair<S, T> b) {
  return make_pair(a.first + b.first, a.second + b.second);
}
template <typename S, typename T>
pair<S, T> operator-(pair<S, T> a, pair<S, T> b) {
  return make_pair(a.first - b.first, a.second - b.second);
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n;
  cin >> n;
  cout << n + n / 2 << endl;
  return 0;
}
