using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Парична_награда
{
	class Program
	{
		static void Main(string[] args)
		{
			int partsProjects = int.Parse(Console.ReadLine());
			double priceForPoint = double.Parse(Console.ReadLine());
			var sum = 0;
			
			var TotalPrice = 0.0;
			for (int i = 0; i < partsProjects; i++)
			{
				var points = int.Parse(Console.ReadLine());
				if (points % 2 == 0)
				{
					points= points * 2;
					
				}
				else
				{
					points++;
					
				}
				sum +=points;
				TotalPrice = (sum * priceForPoint) ;
			}
			
			Console.WriteLine($"{TotalPrice:F2}");
		}
	}
}