Smart Lili

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

namespace _04.Smart_Lili
{
    class SmartLili
    {
        static void Main(string[] args)
        {
            int years = int.Parse(Console.ReadLine());
            double price = double.Parse(Console.ReadLine());
            int toyPrice = int.Parse(Console.ReadLine());
            var brother = 0;
            var toy = 0;
            var toySum = 0;
            double sum = 0;
            var count = 0;
            double result = 0;

            for (int i = 1; i <= years; i++)
            {
                if (i % 2 == 0)
                {
                    count = 10 * ((i+1)/2);
                    sum = sum + count;
                    brother++;
                }
                else
                {
                    toy++;
                }
            }
            toySum = toyPrice * toy;
            sum = sum + toySum - brother;
            result = Math.Abs(sum - price);
            if (sum >= price)
            {
                Console.WriteLine("Yes! {0:f2}",result);
            }
            else
            {
                Console.WriteLine("No! {0:f2}", result);
            }
        }
    }
}