#include <bits/stdc++.h>
using namespace std;
const long long OO = 1e8;
const double EPS = (1e-7);
int dcmp(double x, double y) { return fabs(x - y) <= EPS ? 0 : x < y ? -1 : 1; }
const int N = 100;
bool adjMatrixBool[N][N];
int adjMatrix[N][N];
vector<int> adjMatrixAll[N][N];
map<pair<int, int>, int> adjMatrixMap;
vector<vector<int> > adjList1;
vector<vector<pair<int, int> > > adjList2;
vector<bool> visited;
bool valid(int i, int j) { return 1; }
bool prime(long long n) {
  long long i;
  for (i = 2; i <= sqrt(n); i++) {
    if (n % i == 0) return false;
  }
  return true;
}
long long gcd(long long a, long long b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
long long lcm(long long a, long long b) { return (a / gcd(a, b) * b); }
string int_to_str(int num) {
  stringstream ss;
  ss << num;
  return ss.str();
}
char s[120][120];
int main() {
  ios_base::sync_with_stdio(false);
  long long n;
  cin >> n;
  cout << n + n / 2 << endl;
  return 0;
}
