
import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.Scanner;

public class Main {

  public static void main(String[] args) {

    Scanner sc = new Scanner(System.in);
    // スペース区切りの整数の入力
    BigDecimal R = new BigDecimal(sc.nextInt());
    BigDecimal S = R.multiply(new BigDecimal(2)).setScale(100, RoundingMode.HALF_UP);

    System.out.println(S.multiply(new BigDecimal("3.1415")).setScale(100, RoundingMode.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