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

namespace House_Price
{
	class Program
	{
		static void Main(string[] args)
		{
			double areaSmallRoom = double.Parse(Console.ReadLine());
			double areaKitchen = double.Parse(Console.ReadLine());
			double PriceArea = double.Parse(Console.ReadLine());
			double bathroom = areaSmallRoom /2;
			double areaSecondRoom =(areaSmallRoom *0.1)+areaSmallRoom ;
			double areaThirdRoom = (areaSecondRoom *0.1)+ areaSecondRoom;
			double area = (areaSmallRoom + areaKitchen + bathroom + areaSecondRoom + areaThirdRoom);
			double koridor = area%5;
			double result = area + koridor;
			double Price = result * PriceArea;
			Console.WriteLine("{0:f2}",Price);
		}
	}
}