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

public class Main {

	public static void main(String[] args) throws IOException{
		// TODO Auto-generated method stub
		BufferedReader bfr= new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer str = new StringTokenizer(bfr.readLine());
		int R = Integer.parseInt(str.nextToken());
		double answer = 2*(3.141592)*R;
		System.out.println(answer);
	}

} import java.io.BufferedReader; BufferedReader java.io import java.io.IOException; IOException java.io import java.io.InputStreamReader; InputStreamReader java.io import java.util.StringTokenizer; StringTokenizer java.util public class Main {

	public static void main(String[] args) throws IOException{
		// TODO Auto-generated method stub
		BufferedReader bfr= new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer str = new StringTokenizer(bfr.readLine());
		int R = Integer.parseInt(str.nextToken());
		double answer = 2*(3.141592)*R;
		System.out.println(answer);
	}

} Main public static void main(String[] args) throws IOException{
		// TODO Auto-generated method stub
		BufferedReader bfr= new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer str = new StringTokenizer(bfr.readLine());
		int R = Integer.parseInt(str.nextToken());
		double answer = 2*(3.141592)*R;
		System.out.println(answer);
	} main {
		// TODO Auto-generated method stub
		BufferedReader bfr= new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer str = new StringTokenizer(bfr.readLine());
		int R = Integer.parseInt(str.nextToken());
		double answer = 2*(3.141592)*R;
		System.out.println(answer);
	} BufferedReader bfr= new BufferedReader(new InputStreamReader(System.in)); bfr new BufferedReader(new InputStreamReader(System.in)) StringTokenizer str = new StringTokenizer(bfr.readLine()); str new StringTokenizer(bfr.readLine()) int R = Integer.parseInt(str.nextToken()); R Integer.parseInt(str.nextToken()) Integer.parseInt Integer str.nextToken() str.nextToken str double answer = 2*(3.141592)*R; answer 2*(3.141592)*R 2*(3.141592)*R 2 (3.141592) R System.out.println(answer) System.out.println System.out System System.out answer String[] args args public class Main {

	public static void main(String[] args) throws IOException{
		// TODO Auto-generated method stub
		BufferedReader bfr= new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer str = new StringTokenizer(bfr.readLine());
		int R = Integer.parseInt(str.nextToken());
		double answer = 2*(3.141592)*R;
		System.out.println(answer);
	}

} public class Main {

	public static void main(String[] args) throws IOException{
		// TODO Auto-generated method stub
		BufferedReader bfr= new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer str = new StringTokenizer(bfr.readLine());
		int R = Integer.parseInt(str.nextToken());
		double answer = 2*(3.141592)*R;
		System.out.println(answer);
	}

} Main
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Main {

	public static void main(String[] args) throws IOException{
		// TODO Auto-generated method stub
		BufferedReader bfr= new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer str = new StringTokenizer(bfr.readLine());
		int R = Integer.parseInt(str.nextToken());
		double answer = 2*(3.141592)*R;
		System.out.println(answer);
	}

}
