#include <iostream>
#include <vector>
#include <string>
#include <set>
#include <map>
#include <algorithm>
#include <iomanip>

const int mod=1e9+7;
using LL=long long;
using std::cout;using std::endl;using std::cin;
using std::vector;using std::string;using std::set;using std::multiset;
using std::pair;using std::map;
using std::min;using std::max;
using std::make_pair;
std::ostream& operator<<(std::ostream& os,std::map<int,int>& obj){for(std::map<int,int>::iterator itr=obj.begin();itr!=obj.end();itr++){os<<itr->first<<"^"<<itr->second<<" ";}return os;}
std::ostream& operator<<(std::ostream& os,std::vector<std::map<int,int>>& obj){for(auto itr=obj.begin();itr!=obj.end();itr++){os<<*itr<<std::endl;}return os;}
std::ostream& operator<<(std::ostream& os,std::vector<int>& obj){for(auto itr=obj.begin();itr!=obj.end();itr++){os<<*itr<<endl;}return os;}

namespace ndifix{
template<class T>void sort(T &v){std::sort(v.begin(),v.end());}

}

int main(){std::cout << std::setprecision(10);
  int n,m;cin>>n;
  cout<<(n/2)*3+n%2<<endl;
}