import java.util.*;

class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);

    int r = sc.nextInt();

    // 2×半径×円周率
    double circle = 2 * r * Math.PI;
    System.out.println(circle);

    sc.close();
  }
} import java.util.*; util.* java class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);

    int r = sc.nextInt();

    // 2×半径×円周率
    double circle = 2 * r * Math.PI;
    System.out.println(circle);

    sc.close();
  }
} Main public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);

    int r = sc.nextInt();

    // 2×半径×円周率
    double circle = 2 * r * Math.PI;
    System.out.println(circle);

    sc.close();
  } main {
    Scanner sc = new Scanner(System.in);

    int r = sc.nextInt();

    // 2×半径×円周率
    double circle = 2 * r * Math.PI;
    System.out.println(circle);

    sc.close();
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int r = sc.nextInt(); r sc.nextInt() sc.nextInt sc double circle = 2 * r * Math.PI; circle 2 * r * Math.PI 2 * r * Math.PI 2 r Math.PI Math Math.PI System.out.println(circle) System.out.println System.out System System.out circle sc.close() sc.close sc String[] args args
import java.util.*;

class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);

    int r = sc.nextInt();

    // 2×半径×円周率
    double circle = 2 * r * Math.PI;
    System.out.println(circle);

    sc.close();
  }
}
