import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main
{
	public static void main(String[] Arguments) throws IOException 
	{
		BufferedReader BR = new BufferedReader(new InputStreamReader(System.in));
		int R = Integer.parseInt(BR.readLine());
		System.out.println((double)2 * (double)R * (double)3.1415);
	}
} import java.io.BufferedReader; BufferedReader java.io import java.io.IOException; IOException java.io import java.io.InputStreamReader; InputStreamReader java.io public class Main
{
	public static void main(String[] Arguments) throws IOException 
	{
		BufferedReader BR = new BufferedReader(new InputStreamReader(System.in));
		int R = Integer.parseInt(BR.readLine());
		System.out.println((double)2 * (double)R * (double)3.1415);
	}
} Main public static void main(String[] Arguments) throws IOException 
	{
		BufferedReader BR = new BufferedReader(new InputStreamReader(System.in));
		int R = Integer.parseInt(BR.readLine());
		System.out.println((double)2 * (double)R * (double)3.1415);
	} main {
		BufferedReader BR = new BufferedReader(new InputStreamReader(System.in));
		int R = Integer.parseInt(BR.readLine());
		System.out.println((double)2 * (double)R * (double)3.1415);
	} BufferedReader BR = new BufferedReader(new InputStreamReader(System.in)); BR new BufferedReader(new InputStreamReader(System.in)) int R = Integer.parseInt(BR.readLine()); R Integer.parseInt(BR.readLine()) Integer.parseInt Integer BR.readLine() BR.readLine BR System.out.println((double)2 * (double)R * (double)3.1415) System.out.println System.out System System.out (double)2 * (double)R * (double)3.1415 (double)2 * (double)R * (double)3.1415 (double)2 (double)R (double)3.1415 String[] Arguments Arguments public class Main
{
	public static void main(String[] Arguments) throws IOException 
	{
		BufferedReader BR = new BufferedReader(new InputStreamReader(System.in));
		int R = Integer.parseInt(BR.readLine());
		System.out.println((double)2 * (double)R * (double)3.1415);
	}
} public class Main
{
	public static void main(String[] Arguments) throws IOException 
	{
		BufferedReader BR = new BufferedReader(new InputStreamReader(System.in));
		int R = Integer.parseInt(BR.readLine());
		System.out.println((double)2 * (double)R * (double)3.1415);
	}
} Main
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main
{
	public static void main(String[] Arguments) throws IOException 
	{
		BufferedReader BR = new BufferedReader(new InputStreamReader(System.in));
		int R = Integer.parseInt(BR.readLine());
		System.out.println((double)2 * (double)R * (double)3.1415);
	}
}
