import java.util.*;
import java.math.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sn = new Scanner(System.in);
        
        int r = sn.nextInt();
        BigDecimal num = BigDecimal.valueOf(r * 6.28);
        
        System.out.println(num);

    }
} import java.util.*; util.* java import java.math.*; math.* java public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sn = new Scanner(System.in);
        
        int r = sn.nextInt();
        BigDecimal num = BigDecimal.valueOf(r * 6.28);
        
        System.out.println(num);

    }
} Main public static void main(String[] args) throws Exception {
        Scanner sn = new Scanner(System.in);
        
        int r = sn.nextInt();
        BigDecimal num = BigDecimal.valueOf(r * 6.28);
        
        System.out.println(num);

    } main {
        Scanner sn = new Scanner(System.in);
        
        int r = sn.nextInt();
        BigDecimal num = BigDecimal.valueOf(r * 6.28);
        
        System.out.println(num);

    } Scanner sn = new Scanner(System.in); sn new Scanner(System.in) int r = sn.nextInt(); r sn.nextInt() sn.nextInt sn BigDecimal num = BigDecimal.valueOf(r * 6.28); num BigDecimal.valueOf(r * 6.28) BigDecimal.valueOf BigDecimal r * 6.28 r 6.28 System.out.println(num) System.out.println System.out System System.out num String[] args args public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sn = new Scanner(System.in);
        
        int r = sn.nextInt();
        BigDecimal num = BigDecimal.valueOf(r * 6.28);
        
        System.out.println(num);

    }
} public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sn = new Scanner(System.in);
        
        int r = sn.nextInt();
        BigDecimal num = BigDecimal.valueOf(r * 6.28);
        
        System.out.println(num);

    }
} Main
import java.util.*;
import java.math.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sn = new Scanner(System.in);
        
        int r = sn.nextInt();
        BigDecimal num = BigDecimal.valueOf(r * 6.28);
        
        System.out.println(num);

    }
}
