source_code: import java.io.*;
  import java.util.*;
  
  public class A{     
          
          private BufferedReader in;  
          private StringTokenizer st;
          
          void solve() throws IOException{
              
              int n = nextInt();
              System.out.println(3 * n/2);
          }
              
  
          A() throws IOException {
              in = new BufferedReader(new InputStreamReader(System.in));          
              eat("");
              solve();            
          }
  
          private void eat(String str) {
              st = new StringTokenizer(str);
          }
  
          String next() throws IOException {
              while (!st.hasMoreTokens()) {
                  String line = in.readLine();
                  if (line == null) {
                      return null;
                  }
                  eat(line);
              }
              return st.nextToken();
          }
  
          int nextInt() throws IOException {
              return Integer.parseInt(next());
          }
  
          long nextLong() throws IOException {
              return Long.parseLong(next());
          }
  
          double nextDouble() throws IOException {
              return Double.parseDouble(next());
          }
  
          public static void main(String[] args) throws IOException {
              new A();
          }
  
          int gcd(int a,int b){
              if(b>a) return gcd(b,a);
              if(b==0) return a;
              return gcd(b,a%b);
          }
  
  }
  