#include <bits/stdc++.h>
using namespace std;
using ll = long long int;
ll BIG = 1e18 + 1;
ll MOD = 1e9 + 7;
void solve();
ll fastpow(ll x, ll y, ll n = BIG) {
  x %= n;
  ll ans = 1;
  while (y > 0) {
    if (y & 1) ans = (ans * x) % n;
    x = (x * x) % n;
    y >>= 1;
  }
  return ans;
}
bool sortPairVal(pair<ll, ll> &a, pair<ll, ll> &b) {
  return a.second < b.second;
}
bool sortPairIndex(pair<ll, ll> &a, pair<ll, ll> &b) {
  return a.first < b.first;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  solve();
  return 0;
}
void solve() {
  int t;
  cin >> t;
  cout << t + t / 2 << '\n';
}
