import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		
		double n = sc.nextDouble();
		

		double ans = 2*n*3.14;
		
		System.out.println(ans);
	}
} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		
		double n = sc.nextDouble();
		

		double ans = 2*n*3.14;
		
		System.out.println(ans);
	}
} Main public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		
		double n = sc.nextDouble();
		

		double ans = 2*n*3.14;
		
		System.out.println(ans);
	} main {

		Scanner sc = new Scanner(System.in);
		
		double n = sc.nextDouble();
		

		double ans = 2*n*3.14;
		
		System.out.println(ans);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double n = sc.nextDouble(); n sc.nextDouble() sc.nextDouble sc double ans = 2*n*3.14; ans 2*n*3.14 2*n*3.14 2 n 3.14 System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		
		double n = sc.nextDouble();
		

		double ans = 2*n*3.14;
		
		System.out.println(ans);
	}
} public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		
		double n = sc.nextDouble();
		

		double ans = 2*n*3.14;
		
		System.out.println(ans);
	}
} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		
		double n = sc.nextDouble();
		

		double ans = 2*n*3.14;
		
		System.out.println(ans);
	}
}
