import java.util.*;
import java.math.*;
import java.io.*;

public class Main{
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int tt = in.nextInt();
		double a = Math.PI*2*tt;
		System.out.println(String.format("%.20f", a));
	}
} import java.util.*; util.* java import java.math.*; math.* java import java.io.*; io.* java public class Main{
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int tt = in.nextInt();
		double a = Math.PI*2*tt;
		System.out.println(String.format("%.20f", a));
	}
} Main public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int tt = in.nextInt();
		double a = Math.PI*2*tt;
		System.out.println(String.format("%.20f", a));
	} main {
		Scanner in = new Scanner(System.in);
		int tt = in.nextInt();
		double a = Math.PI*2*tt;
		System.out.println(String.format("%.20f", a));
	} Scanner in = new Scanner(System.in); in new Scanner(System.in) int tt = in.nextInt(); tt in.nextInt() in.nextInt in double a = Math.PI*2*tt; a Math.PI*2*tt Math.PI*2*tt Math.PI Math Math.PI 2 tt System.out.println(String.format("%.20f", a)) System.out.println System.out System System.out String.format("%.20f", a) String.format String "%.20f" a String[] args args public class Main{
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int tt = in.nextInt();
		double a = Math.PI*2*tt;
		System.out.println(String.format("%.20f", a));
	}
} public class Main{
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int tt = in.nextInt();
		double a = Math.PI*2*tt;
		System.out.println(String.format("%.20f", a));
	}
} Main
import java.util.*;
import java.math.*;
import java.io.*;

public class Main{
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int tt = in.nextInt();
		double a = Math.PI*2*tt;
		System.out.println(String.format("%.20f", a));
	}
}