import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        double num = sc.nextDouble();
        System.out.println(2 * Math.PI * num);
    }
} import java.io.File; File java.io import java.io.FileInputStream; FileInputStream java.io import java.io.FileNotFoundException; FileNotFoundException java.io import java.util.*; util.* java public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        double num = sc.nextDouble();
        System.out.println(2 * Math.PI * num);
    }
} Main public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        double num = sc.nextDouble();
        System.out.println(2 * Math.PI * num);
    } main {
        Scanner sc = new Scanner(System.in);
        double num = sc.nextDouble();
        System.out.println(2 * Math.PI * num);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double num = sc.nextDouble(); num sc.nextDouble() sc.nextDouble sc System.out.println(2 * Math.PI * num) System.out.println System.out System System.out 2 * Math.PI * num 2 * Math.PI * num 2 Math.PI Math Math.PI num String[] args args public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        double num = sc.nextDouble();
        System.out.println(2 * Math.PI * num);
    }
} public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        double num = sc.nextDouble();
        System.out.println(2 * Math.PI * num);
    }
} Main
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        double num = sc.nextDouble();
        System.out.println(2 * Math.PI * num);
    }
}
