#include<bits/stdc++.h>             
using namespace std;                
typedef long long ll;               
                                    
signed main()                       
{                                   
  cin.tie(0);                       
  ios::sync_with_stdio(false);      
                                    
  int n; cin >> n;                  
  double j = 1.5 * n;               
  cout << (int)j << '\n';           
                                    
  return 0;                         
}