public class Main{
 public static void main(String[] args){
   int R = new java.util.Scanner ( System.in ).nextInt ();
   double enshu = 2 * Math.PI * R;
   System.out.println(enshu);
 }
}
/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