import java.util.*;
class Main {
    public static void main(String[] args) {
        Scanner rv=new Scanner(System.in);
        int r;
        r=rv.nextInt();
        System.out.println(2*3.14*r);
    }
} import java.util.*; util.* java class Main {
    public static void main(String[] args) {
        Scanner rv=new Scanner(System.in);
        int r;
        r=rv.nextInt();
        System.out.println(2*3.14*r);
    }
} Main public static void main(String[] args) {
        Scanner rv=new Scanner(System.in);
        int r;
        r=rv.nextInt();
        System.out.println(2*3.14*r);
    } main {
        Scanner rv=new Scanner(System.in);
        int r;
        r=rv.nextInt();
        System.out.println(2*3.14*r);
    } Scanner rv=new Scanner(System.in); rv new Scanner(System.in) int r; r r=rv.nextInt() r rv.nextInt() rv.nextInt rv System.out.println(2*3.14*r) System.out.println System.out System System.out 2*3.14*r 2*3.14*r 2 3.14 r String[] args args
import java.util.*;
class Main {
    public static void main(String[] args) {
        Scanner rv=new Scanner(System.in);
        int r;
        r=rv.nextInt();
        System.out.println(2*3.14*r);
    }
}