#include <algorithm>
#include <cmath>
#include <cstdio>
#include <deque>
#include <iomanip>
#include <iostream>
#include <queue>
#include <stack>
#include <utility>
#include <vector>
using std::cerr;
using std::cin;
using std::cout;
using std::endl;

int main(void) {
  cout << std::fixed << std::setprecision(10);
  cin.tie(0);
  std::ios::sync_with_stdio(false);
  int n;
  cin >> n;
  double amount = n * 1.5;
  cout << (int)floor(amount) << endl;

  return 0;
}