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

class Magatro
{
    static void Main()
    {
        int C = int.Parse(Console.ReadLine());
        int IN, OUT;
        string[] s = Console.ReadLine().Split(' ');
        IN = int.Parse(s[0]);
        OUT = int.Parse(s[1]);
        double danmen = (OUT - IN) * (OUT - IN)/4.0 * Math.PI;
        double enshu = (OUT + IN) * Math.PI;
        Console.WriteLine(danmen * enshu * C);
    }
}