import java.util.Scanner;

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

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