#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <iomanip>
#include <cmath>
#include <stdio.h>
#include <queue>
#include <deque>
#include <cstdio>
#include <set>
#include <map>
#include <bitset>
#include <stack>
#include <cctype>
#define rep(i,N) for (int i = 0; i < (N); i++)
using ll = long long;
using lb = long double;
using namespace std;
const int mod = 1000000007;

ll gcd(ll P, ll Q){
  return Q ? gcd(Q,P % Q):P;
}

ll lcm(ll P, ll Q){
  return P / gcd(P,Q) * Q;
}

string change_big(string str){
  transform(str.begin(), str.end(), str.begin(), ::toupper);
  return str;
}

string change_small(string str){
  transform(str.begin(), str.end(), str.begin(), ::tolower);
  return str;
}

bool is_prime(int x){
  if(x<=1) return false;
  for(int i=2;i*i<=x;i++)
    if(x%i==0) return false;
  return true;
}

ll sum_of_num(ll num){
  ll dig;
  ll sum = 0;
  while(num){
    dig = num % 10;
    sum = sum + dig;
    num = num / 10;
  }
  return sum;
}

ll how_many_break(ll n, ll m){
  ll counter = 0;
  while (n % m == 0){
    n = n / m;
    counter++;
  }
  return counter;
}

/*------------------------------------------------------------------------------------*/

int main(){
  ll N;
  cin >> N;
  ll P = N * 3 / 2;
  cout << P << endl;
  return 0;
}