import java.util.*;
public class Metode4{
	static double obKr(double r){  //obseg Kroga
		double o = Math.PI*2*r;
		return o;
	}
	
	public static void main(String[]args){
		Scanner sc = new Scanner(System.in);
		System.out.print("Vnesi r kroga: ");
		double r = sc.nextDouble();
		//klic metode
		System.out.println("Obseg kroga je: "+obKr(r));
	}
}