import java.util.Scanner;

public class Main{
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int i = scanner.nextInt();
        double ans = 2*Math.PI*i;
        System.out.println(ans);
    }
} import java.util.Scanner; Scanner java.util public class Main{
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int i = scanner.nextInt();
        double ans = 2*Math.PI*i;
        System.out.println(ans);
    }
} Main public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int i = scanner.nextInt();
        double ans = 2*Math.PI*i;
        System.out.println(ans);
    } main {
        Scanner scanner = new Scanner(System.in);
        int i = scanner.nextInt();
        double ans = 2*Math.PI*i;
        System.out.println(ans);
    } Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) int i = scanner.nextInt(); i scanner.nextInt() scanner.nextInt scanner double ans = 2*Math.PI*i; ans 2*Math.PI*i 2*Math.PI*i 2 Math.PI Math Math.PI i 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 scanner = new Scanner(System.in);
        int i = scanner.nextInt();
        double ans = 2*Math.PI*i;
        System.out.println(ans);
    }
} public class Main{
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int i = scanner.nextInt();
        double ans = 2*Math.PI*i;
        System.out.println(ans);
    }
} Main
import java.util.Scanner;

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