    import java.util.Scanner;
    import java.lang.Math;
    import java.math.BigDecimal;
     
    class Main{
     
        public static void main(String[] args){
     
            Scanner scanner = new Scanner(System.in);
            int r = scanner.nextInt();
            scanner.close();
            BigDecimal bd1 = new BigDecimal(2.0 * r);
            BigDecimal bd2 = new BigDecimal(Math.PI);
            BigDecimal result = bd1.multiply(bd2);
            System.out.println(result.setScale(2, BigDecimal.ROUND_HALF_UP));
     
        }
     
    }
/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