ATM Machine program in C#.Net

using System;
namespace atm_program
{
	class ab
	{
		static void Main(String[] args)
		{
			int amt=10000,a,current,pin=4040,pin1,pin2;

			//read PIN
			Console.WriteLine("Enter the pin");
			pin1=int.Parse(Console.ReadLine());

			//compare PIN
			if(pin1==pin)
			{
				Console.WriteLine("1.To check balance");
				Console.WriteLine("2.To withdraw money");
				Console.WriteLine("3.To deposite Money");
				Console.WriteLine("4.To change the pin");
				Console.WriteLine("Enter your choice");
				int ch=int.Parse(Console.ReadLine());
				switch(ch)
				{
					case 1:
						Console.WriteLine("The current balance in your account is"+amt);
					break;
					
					case 2:
					Console.WriteLine("Enter the amount to withdraw");
					{
						a=int.Parse(Console.ReadLine());
						if(amt>=a)
						{
							if(a%100==0)
							{
								Console.WriteLine("Please collect the cash"+a);
								current=amt-a;
								Console.WriteLine("The current balance is now"+current);
							}
							else
								Console.WriteLine("Please enter the amount to withdraw in the multiples of 100");
						}
						else
						Console.WriteLine("Your account does not have sufficient balance");
					}

					break;

					case 3:
					Console.WriteLine("Enter the amount to be deposite");
					a=int.Parse(Console.ReadLine());
					current=amt+a;
					Console.WriteLine("The current balance in the account is"+current);
					break;
					
					case 4:
					Console.WriteLine("Want to change your pin");
					Console.WriteLine("Enter your previous pin");
					int prepin=int.Parse(Console.ReadLine());
					if(prepin==pin)
					{
						Console.WriteLine("Enter your new pin");
						pin2=int.Parse(Console.ReadLine());
						pin1=pin2;
						Console.WriteLine("Your pin is changed");
					}
					else
						Console.WriteLine("Enter your correct pin");
					break;
					
					default:
					Console.WriteLine("Please select correct option");
					break;
				}
			}
			else
				Console.WriteLine("Pin is wrong");
		}
	}
}

Output