giftbox coverage

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Threading;

namespace ConsoleApp1
{
    class Exam
    {
        static void Main(string[] args)
        {
            double a = double.Parse(Console.ReadLine());
            double sheets = double.Parse(Console.ReadLine());
            double sheetArea = double.Parse(Console.ReadLine());
            double allSheatArea = 0;

            double boxArea = a * a * 6;

                for (int i = 1; i <= sheets; i++)
                {
                    if (i % 3 == 0)
                    {
                        allSheatArea += sheetArea * 0.25;
                    }
                    else
                    {
                        allSheatArea += sheetArea;
                    }
                }

            double percentage = allSheatArea / boxArea * 100.0;

            Console.WriteLine($"You can cover {percentage:f2}% of the box.");
        }
    }
}