import java.io.*;
import java.util.*;
import java.lang.*;
import java.math.*;
public class Main{

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int R=in.nextInt();
		in.close();
		double result=2*R*Math.PI;
		System.out.println(result);
	}

} import java.io.*; io.* java import java.util.*; util.* java import java.lang.*; lang.* java import java.math.*; math.* java public class Main{

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int R=in.nextInt();
		in.close();
		double result=2*R*Math.PI;
		System.out.println(result);
	}

} Main public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int R=in.nextInt();
		in.close();
		double result=2*R*Math.PI;
		System.out.println(result);
	} main {
		Scanner in = new Scanner(System.in);
		int R=in.nextInt();
		in.close();
		double result=2*R*Math.PI;
		System.out.println(result);
	} Scanner in = new Scanner(System.in); in new Scanner(System.in) int R=in.nextInt(); R in.nextInt() in.nextInt in in.close() in.close in double result=2*R*Math.PI; result 2*R*Math.PI 2*R*Math.PI 2 R Math.PI Math Math.PI System.out.println(result) System.out.println System.out System System.out result String[] args args public class Main{

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int R=in.nextInt();
		in.close();
		double result=2*R*Math.PI;
		System.out.println(result);
	}

} public class Main{

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int R=in.nextInt();
		in.close();
		double result=2*R*Math.PI;
		System.out.println(result);
	}

} Main
import java.io.*;
import java.util.*;
import java.lang.*;
import java.math.*;
public class Main{

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int R=in.nextInt();
		in.close();
		double result=2*R*Math.PI;
		System.out.println(result);
	}

}
