    import java.util.*;
    public class Main{
         
          public static void main(String []args){
            Scanner in = new Scanner(System.in);
          double PI = 2 * Math.acos(0.0);
            int r = in.nextInt();
            System.out.println(2 * PI * r);
          }
        }
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz