using System;

namespace _02._Circle_Area__Precision_12_
{
    class Program
    {
        static void Main(string[] args)
        {
            //Write program to enter a radius r (real number) and print the area of the circle with exactly 12 digits after the decimal 
            //point. Use data type of enough precision to hold the results.
            double radius = double.Parse(Console.ReadLine());
            double area = Math.PI * Math.Pow(radius, 2);
            Console.WriteLine($"{area:f12}");
        }
    }
}