using System;
using System.Linq;

public class Program {
    public static void Main() {
        int cal = int.Parse(Console.ReadLine());
        int[] rad = Array.ConvertAll(Console.ReadLine().Split(), value => int.Parse(value));    //内径、外径
        double csRad = (rad[1]-rad[0])/2.0; //断面の半径
        double PI = 3.14159265358979323846264338327950288;
        double surface = csRad * csRad * PI;    //断面積
        double v = surface * rad.Sum()*PI;  //体積
        Console.WriteLine(v * cal);
    }
}