source_code: 
  import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.io.OutputStreamWriter;
  import java.io.PrintWriter;
  
  public class TemplateBuf implements Runnable{
      
      private void solve() throws Exception {
          long n = nextUnsignedLong();
          
          out.println(n+n/2);
      }
  
      /////////////////////////////////////////////////
      
      BufferedReader in;
      PrintWriter out;
      
      @Override
      public void run() {
          try{
              in = new BufferedReader(new InputStreamReader(System.in), INPUT_BUF_SIZE);
              out = new PrintWriter(new OutputStreamWriter(System.out));
              solve();
              out.flush();
          }catch (Exception e) {
              e.printStackTrace();
              System.exit(1);
          }
      }
      
      final int INPUT_BUF_SIZE = 1024 * 8;
      final int BUF_SIZE = INPUT_BUF_SIZE;
      char[] buf = new char[BUF_SIZE];
      int ch=-1;
      int charRead=-1;
      int charPos=-1;
      
      public char nextChar() throws IOException{
          if (charPos<0 || charPos>=charRead){
              charRead = in.read(buf);
              charPos=0;
          }
          return buf[charPos++];
      }
      
      public long nextUnsignedLong() throws IOException{      
          while ((ch=nextChar())<'0' || ch>'9');
          long num = ch-'0';
          while ((ch=nextChar())>='0' && ch<='9'){
              num*=10;
              num+=ch-'0';
          }
          return num;
      }
      
      public int nextUnsignedInt() throws IOException{
          return (int)nextUnsignedLong();
      }
      
      public double nextDouble() throws IOException{
          while (((ch=nextChar())<'0' || ch>'9') && ch!='.' && ch!='-');
          char[] tmp = new char[255];
          int itmp = 0;
          tmp[itmp++]=(char)ch;
          while (((ch=nextChar())>='0' && ch<='9') || ch=='.' || ch=='-'){
              tmp[itmp++]=(char)ch;
          }
          return Double.parseDouble(new String(tmp,0,itmp));
      }
      
      public static void main(String[] args) {
          new TemplateBuf().run();
      }
      
  }
  