import java.util.*;
class Main{
    static public void main(String args[])
    {
        Scanner in = new Scanner(System.in);
        int R = in.nextInt();
        
        double pie = (double)22/7;
        System.out.println(pie*2*R - 0.01);
    }
} import java.util.*; util.* java class Main{
    static public void main(String args[])
    {
        Scanner in = new Scanner(System.in);
        int R = in.nextInt();
        
        double pie = (double)22/7;
        System.out.println(pie*2*R - 0.01);
    }
} Main static public void main(String args[])
    {
        Scanner in = new Scanner(System.in);
        int R = in.nextInt();
        
        double pie = (double)22/7;
        System.out.println(pie*2*R - 0.01);
    } main {
        Scanner in = new Scanner(System.in);
        int R = in.nextInt();
        
        double pie = (double)22/7;
        System.out.println(pie*2*R - 0.01);
    } Scanner in = new Scanner(System.in); in new Scanner(System.in) int R = in.nextInt(); R in.nextInt() in.nextInt in double pie = (double)22/7; pie (double)22/7 (double)22 7 System.out.println(pie*2*R - 0.01) System.out.println System.out System System.out pie*2*R - 0.01 pie*2*R pie*2*R pie 2 R 0.01 String args[] args
import java.util.*;
class Main{
    static public void main(String args[])
    {
        Scanner in = new Scanner(System.in);
        int R = in.nextInt();
        
        double pie = (double)22/7;
        System.out.println(pie*2*R - 0.01);
    }
}