using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static string[] SList(long n) => Enumerable.Repeat(0, (int)n).Select(_ => ReadLine()).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var c = NN;
        var s = NList;
        var sr = (s[1] - s[0]) * 0.5;
        var lr = (s[0] + s[1]) * 0.5;
        WriteLine(sr * sr * Math.PI * lr * 2 * Math.PI * c);
    }
}