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) {
			FastScanner fsc = new FastScanner();

			int Radius = fsc.nextInt();

			int  Diameter = Radius * 2;
			//Math.PIは円周率定数
			double anser = Diameter * Math.PI;
			System.out.println(anser);

	}

}

class FastScanner {

	BufferedReader br;

	StringTokenizer st;



	public FastScanner() {

		br = new BufferedReader(new InputStreamReader(System.in));

	}



	String next() {

		while (st == null || !st.hasMoreElements()) {

			try {

				st = new StringTokenizer(br.readLine());

			} catch (IOException e) {

				e.printStackTrace();

			}

		}

		return st.nextToken();

	}



	int nextInt() {

		return Integer.parseInt(next());

	}



	long nextLong() {

		return Long.parseLong(next());

	}

} 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) {
			FastScanner fsc = new FastScanner();

			int Radius = fsc.nextInt();

			int  Diameter = Radius * 2;
			//Math.PIは円周率定数
			double anser = Diameter * Math.PI;
			System.out.println(anser);

	}

} Main public static void main(String[] args) {
			FastScanner fsc = new FastScanner();

			int Radius = fsc.nextInt();

			int  Diameter = Radius * 2;
			//Math.PIは円周率定数
			double anser = Diameter * Math.PI;
			System.out.println(anser);

	} main {
			FastScanner fsc = new FastScanner();

			int Radius = fsc.nextInt();

			int  Diameter = Radius * 2;
			//Math.PIは円周率定数
			double anser = Diameter * Math.PI;
			System.out.println(anser);

	} FastScanner fsc = new FastScanner(); fsc new FastScanner() int Radius = fsc.nextInt(); Radius fsc.nextInt() fsc.nextInt fsc int  Diameter = Radius * 2; Diameter Radius * 2 Radius 2 double anser = Diameter * Math.PI; anser Diameter * Math.PI Diameter Math.PI Math Math.PI System.out.println(anser) System.out.println System.out System System.out anser String[] args args class FastScanner {

	BufferedReader br;

	StringTokenizer st;



	public FastScanner() {

		br = new BufferedReader(new InputStreamReader(System.in));

	}



	String next() {

		while (st == null || !st.hasMoreElements()) {

			try {

				st = new StringTokenizer(br.readLine());

			} catch (IOException e) {

				e.printStackTrace();

			}

		}

		return st.nextToken();

	}



	int nextInt() {

		return Integer.parseInt(next());

	}



	long nextLong() {

		return Long.parseLong(next());

	}

} FastScanner BufferedReader br; br StringTokenizer st; st public FastScanner() {

		br = new BufferedReader(new InputStreamReader(System.in));

	} FastScanner {

		br = new BufferedReader(new InputStreamReader(System.in));

	} br = new BufferedReader(new InputStreamReader(System.in)) br new BufferedReader(new InputStreamReader(System.in)) String next() {

		while (st == null || !st.hasMoreElements()) {

			try {

				st = new StringTokenizer(br.readLine());

			} catch (IOException e) {

				e.printStackTrace();

			}

		}

		return st.nextToken();

	} next {

		while (st == null || !st.hasMoreElements()) {

			try {

				st = new StringTokenizer(br.readLine());

			} catch (IOException e) {

				e.printStackTrace();

			}

		}

		return st.nextToken();

	} while (st == null || !st.hasMoreElements()) {

			try {

				st = new StringTokenizer(br.readLine());

			} catch (IOException e) {

				e.printStackTrace();

			}

		} st == null || !st.hasMoreElements() st == null st null !st.hasMoreElements() st.hasMoreElements() st.hasMoreElements st {

			try {

				st = new StringTokenizer(br.readLine());

			} catch (IOException e) {

				e.printStackTrace();

			}

		} try {

				st = new StringTokenizer(br.readLine());

			} catch (IOException e) {

				e.printStackTrace();

			} catch (IOException e) {

				e.printStackTrace();

			} IOException e {

				e.printStackTrace();

			} e.printStackTrace() e.printStackTrace e {

				st = new StringTokenizer(br.readLine());

			} st = new StringTokenizer(br.readLine()) st new StringTokenizer(br.readLine()) return st.nextToken(); st.nextToken() st.nextToken st int nextInt() {

		return Integer.parseInt(next());

	} nextInt {

		return Integer.parseInt(next());

	} return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next long nextLong() {

		return Long.parseLong(next());

	} nextLong {

		return Long.parseLong(next());

	} return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next public class Main {

	public static void main(String[] args) {
			FastScanner fsc = new FastScanner();

			int Radius = fsc.nextInt();

			int  Diameter = Radius * 2;
			//Math.PIは円周率定数
			double anser = Diameter * Math.PI;
			System.out.println(anser);

	}

} public class Main {

	public static void main(String[] args) {
			FastScanner fsc = new FastScanner();

			int Radius = fsc.nextInt();

			int  Diameter = Radius * 2;
			//Math.PIは円周率定数
			double anser = Diameter * Math.PI;
			System.out.println(anser);

	}

} 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) {
			FastScanner fsc = new FastScanner();

			int Radius = fsc.nextInt();

			int  Diameter = Radius * 2;
			//Math.PIは円周率定数
			double anser = Diameter * Math.PI;
			System.out.println(anser);

	}

}

class FastScanner {

	BufferedReader br;

	StringTokenizer st;



	public FastScanner() {

		br = new BufferedReader(new InputStreamReader(System.in));

	}



	String next() {

		while (st == null || !st.hasMoreElements()) {

			try {

				st = new StringTokenizer(br.readLine());

			} catch (IOException e) {

				e.printStackTrace();

			}

		}

		return st.nextToken();

	}



	int nextInt() {

		return Integer.parseInt(next());

	}



	long nextLong() {

		return Long.parseLong(next());

	}

}