Create mask with size n

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

namespace ConsoleApplication4
{
    class Program
    {
        static void Main(string[] args)
        {
            int maskSize = 4 + 1;
            int mask = 1 << maskSize;
            mask -= 1;// when we receive mask - 1 and mask was 10000 the result is 1111 that is why we have to add +1 in the beggining
            Console.WriteLine(mask);
        }
    }
}