import java.util.*;
import java.io.*;
public class Main
{
    static BufferedWriter bw;
    static BufferedReader br;
    static void solve()throws Exception
    {
        int r = Integer.parseInt(br.readLine());
        double result = 2 * 22/7.0 * r;
        bw.write(Double.toString(result));
        bw.newLine();
    }
    public static void main(String []args)throws Exception
    {
        br=new BufferedReader(new InputStreamReader(System.in));
        bw=new BufferedWriter(new OutputStreamWriter(System.out));
        // int t = Integer.parseInt(br.readLine());
        // for(int i=0;i<t;i++)
        // {
        //     bw.write("Case #"+(i+1)+": ");
            solve();
        // }
        br.close();
        bw.close();
    }
} import java.util.*; util.* java import java.io.*; io.* java public class Main
{
    static BufferedWriter bw;
    static BufferedReader br;
    static void solve()throws Exception
    {
        int r = Integer.parseInt(br.readLine());
        double result = 2 * 22/7.0 * r;
        bw.write(Double.toString(result));
        bw.newLine();
    }
    public static void main(String []args)throws Exception
    {
        br=new BufferedReader(new InputStreamReader(System.in));
        bw=new BufferedWriter(new OutputStreamWriter(System.out));
        // int t = Integer.parseInt(br.readLine());
        // for(int i=0;i<t;i++)
        // {
        //     bw.write("Case #"+(i+1)+": ");
            solve();
        // }
        br.close();
        bw.close();
    }
} Main static BufferedWriter bw; bw static BufferedReader br; br static void solve()throws Exception
    {
        int r = Integer.parseInt(br.readLine());
        double result = 2 * 22/7.0 * r;
        bw.write(Double.toString(result));
        bw.newLine();
    } solve {
        int r = Integer.parseInt(br.readLine());
        double result = 2 * 22/7.0 * r;
        bw.write(Double.toString(result));
        bw.newLine();
    } int r = Integer.parseInt(br.readLine()); r Integer.parseInt(br.readLine()) Integer.parseInt Integer br.readLine() br.readLine br double result = 2 * 22/7.0 * r; result 2 * 22/7.0 * r 2 * 22/7.0 2 * 22 2 22 7.0 r bw.write(Double.toString(result)) bw.write bw Double.toString(result) Double.toString Double result bw.newLine() bw.newLine bw public static void main(String []args)throws Exception
    {
        br=new BufferedReader(new InputStreamReader(System.in));
        bw=new BufferedWriter(new OutputStreamWriter(System.out));
        // int t = Integer.parseInt(br.readLine());
        // for(int i=0;i<t;i++)
        // {
        //     bw.write("Case #"+(i+1)+": ");
            solve();
        // }
        br.close();
        bw.close();
    } main {
        br=new BufferedReader(new InputStreamReader(System.in));
        bw=new BufferedWriter(new OutputStreamWriter(System.out));
        // int t = Integer.parseInt(br.readLine());
        // for(int i=0;i<t;i++)
        // {
        //     bw.write("Case #"+(i+1)+": ");
            solve();
        // }
        br.close();
        bw.close();
    } br=new BufferedReader(new InputStreamReader(System.in)) br new BufferedReader(new InputStreamReader(System.in)) bw=new BufferedWriter(new OutputStreamWriter(System.out)) bw new BufferedWriter(new OutputStreamWriter(System.out)) solve() solve br.close() br.close br bw.close() bw.close bw String []args args public class Main
{
    static BufferedWriter bw;
    static BufferedReader br;
    static void solve()throws Exception
    {
        int r = Integer.parseInt(br.readLine());
        double result = 2 * 22/7.0 * r;
        bw.write(Double.toString(result));
        bw.newLine();
    }
    public static void main(String []args)throws Exception
    {
        br=new BufferedReader(new InputStreamReader(System.in));
        bw=new BufferedWriter(new OutputStreamWriter(System.out));
        // int t = Integer.parseInt(br.readLine());
        // for(int i=0;i<t;i++)
        // {
        //     bw.write("Case #"+(i+1)+": ");
            solve();
        // }
        br.close();
        bw.close();
    }
} public class Main
{
    static BufferedWriter bw;
    static BufferedReader br;
    static void solve()throws Exception
    {
        int r = Integer.parseInt(br.readLine());
        double result = 2 * 22/7.0 * r;
        bw.write(Double.toString(result));
        bw.newLine();
    }
    public static void main(String []args)throws Exception
    {
        br=new BufferedReader(new InputStreamReader(System.in));
        bw=new BufferedWriter(new OutputStreamWriter(System.out));
        // int t = Integer.parseInt(br.readLine());
        // for(int i=0;i<t;i++)
        // {
        //     bw.write("Case #"+(i+1)+": ");
            solve();
        // }
        br.close();
        bw.close();
    }
} Main
import java.util.*;
import java.io.*;
public class Main
{
    static BufferedWriter bw;
    static BufferedReader br;
    static void solve()throws Exception
    {
        int r = Integer.parseInt(br.readLine());
        double result = 2 * 22/7.0 * r;
        bw.write(Double.toString(result));
        bw.newLine();
    }
    public static void main(String []args)throws Exception
    {
        br=new BufferedReader(new InputStreamReader(System.in));
        bw=new BufferedWriter(new OutputStreamWriter(System.out));
        // int t = Integer.parseInt(br.readLine());
        // for(int i=0;i<t;i++)
        // {
        //     bw.write("Case #"+(i+1)+": ");
            solve();
        // }
        br.close();
        bw.close();
    }
}
