using System;
using System.Linq;

public class yukicoder
{
    public static void Main()
    {
        double c = int.Parse(Console.ReadLine());
        double[] input = Console.ReadLine().Split(' ').Select(x => double.Parse(x)).ToArray();
        double ins = input[0];
        double outs = input[1];
        double center = (outs - ins) / 2;
        
        double wk = Math.Pow(center, 2) * Math.PI * (center + ins) * 2 * Math.PI;
        
        Console.WriteLine(wk * c);

    }
}