using System;
using System.Collections.Generic;
using System.Text;

public class Program
{
    public void Proc(){
        
        Reader.IsDebug = false;
        double num = long.Parse(Reader.ReadLine());
        num *= 3.5;
        Console.WriteLine(num.ToString("######################.#"));
        
    }
    
    public static void Main(string[] args)
    {
        Program prg = new Program();
        prg.Proc();
    }
}

class Reader
{
    public static bool IsDebug = true;
    
    private static System.IO.StringReader sr;
    
    public static string ReadLine() {
        if(IsDebug) {
            if(sr == null) {
                sr = new System.IO.StringReader(initStr.Trim());
            }
            return sr.ReadLine();
        } else {
            return Console.ReadLine();
        }
    }
    
    public static int[] GetInt(char delimiter = ' ') {
        string[] inpt = ReadLine().Split(delimiter);
        int[] ret = new int[inpt.Length];
        for(int i=0; i<inpt.Length; i++) {
            ret[i] = int.Parse(inpt[i]);
        }
        return ret;
    }
    
    private static string initStr = @"


3


";
}