using System;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        int cal = int.Parse(Console.ReadLine());
        string[] s = Console.ReadLine().Split();
        int inside = int.Parse(s[0]);
        int outside = int.Parse(s[1]);

        double area = (outside - inside) / 2 * (outside - inside) / 2 * Math.PI;
        double radius = (inside + outside) * Math.PI;

        Console.WriteLine(area * radius * cal);
        Console.Read();
    }
}