import java.util.Scanner;

public class Main {
	public static void main (String args[]) throws Exception{
		Scanner scan = new Scanner(System.in);
		double r = scan.nextInt();
		
		double p = 3.1415926535;
		System.out.println(2*r*p);
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main (String args[]) throws Exception{
		Scanner scan = new Scanner(System.in);
		double r = scan.nextInt();
		
		double p = 3.1415926535;
		System.out.println(2*r*p);
	}
} Main public static void main (String args[]) throws Exception{
		Scanner scan = new Scanner(System.in);
		double r = scan.nextInt();
		
		double p = 3.1415926535;
		System.out.println(2*r*p);
	} main {
		Scanner scan = new Scanner(System.in);
		double r = scan.nextInt();
		
		double p = 3.1415926535;
		System.out.println(2*r*p);
	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) double r = scan.nextInt(); r scan.nextInt() scan.nextInt scan double p = 3.1415926535; p 3.1415926535 System.out.println(2*r*p) System.out.println System.out System System.out 2*r*p 2*r*p 2 r p String args[] args public class Main {
	public static void main (String args[]) throws Exception{
		Scanner scan = new Scanner(System.in);
		double r = scan.nextInt();
		
		double p = 3.1415926535;
		System.out.println(2*r*p);
	}
} public class Main {
	public static void main (String args[]) throws Exception{
		Scanner scan = new Scanner(System.in);
		double r = scan.nextInt();
		
		double p = 3.1415926535;
		System.out.println(2*r*p);
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main (String args[]) throws Exception{
		Scanner scan = new Scanner(System.in);
		double r = scan.nextInt();
		
		double p = 3.1415926535;
		System.out.println(2*r*p);
	}
}
