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

class Program
{
    static long NN => long.Parse(ReadLine());
    static long[] NList => ReadLine().Split().Select(long.Parse).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var a = double.Parse(ReadLine());
        var b = double.Parse(ReadLine());
        WriteLine((b - a) * 2 * Math.PI);
    }
}