


import java.util.Scanner;

public class Main {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        int i = sc.nextInt();
        double c =Math.PI*2*i;
        System.out.println(c);
    }
} import java.util.Scanner; Scanner java.util public class Main {

    public static void main(String[] args) {

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

        Scanner sc = new Scanner(System.in);
        int i = sc.nextInt();
        double c =Math.PI*2*i;
        System.out.println(c);
    } main {

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

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        int i = sc.nextInt();
        double c =Math.PI*2*i;
        System.out.println(c);
    }
} public class Main {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        int i = sc.nextInt();
        double c =Math.PI*2*i;
        System.out.println(c);
    }
} Main



import java.util.Scanner;

public class Main {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        int i = sc.nextInt();
        double c =Math.PI*2*i;
        System.out.println(c);
    }
}
