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

public class Main {

	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		int r = Integer.parseInt(br.readLine());

		System.out.println((double) (r * 2 * 3.14));
	}
} 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[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		int r = Integer.parseInt(br.readLine());

		System.out.println((double) (r * 2 * 3.14));
	}
} Main public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		int r = Integer.parseInt(br.readLine());

		System.out.println((double) (r * 2 * 3.14));
	} main {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		int r = Integer.parseInt(br.readLine());

		System.out.println((double) (r * 2 * 3.14));
	} 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) (r * 2 * 3.14)) System.out.println System.out System System.out (double) (r * 2 * 3.14) r * 2 * 3.14 r 2 3.14 String[] args args public class Main {

	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		int r = Integer.parseInt(br.readLine());

		System.out.println((double) (r * 2 * 3.14));
	}
} public class Main {

	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		int r = Integer.parseInt(br.readLine());

		System.out.println((double) (r * 2 * 3.14));
	}
} Main
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {

	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		int r = Integer.parseInt(br.readLine());

		System.out.println((double) (r * 2 * 3.14));
	}
}