import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		int R = sc.nextInt();
        double KO=2*3.14*R;
        System.out.println(KO);
		
	}
} import java.util.*; util.* java public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		int R = sc.nextInt();
        double KO=2*3.14*R;
        System.out.println(KO);
		
	}
} Main public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		int R = sc.nextInt();
        double KO=2*3.14*R;
        System.out.println(KO);
		
	} main {
		Scanner sc = new Scanner(System.in);
		
		int R = sc.nextInt();
        double KO=2*3.14*R;
        System.out.println(KO);
		
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int R = sc.nextInt(); R sc.nextInt() sc.nextInt sc double KO=2*3.14*R; KO 2*3.14*R 2*3.14*R 2 3.14 R System.out.println(KO) System.out.println System.out System System.out KO String[] args args public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		int R = sc.nextInt();
        double KO=2*3.14*R;
        System.out.println(KO);
		
	}
} public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		int R = sc.nextInt();
        double KO=2*3.14*R;
        System.out.println(KO);
		
	}
} Main
import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		int R = sc.nextInt();
        double KO=2*3.14*R;
        System.out.println(KO);
		
	}
}