public void Main()
{	
	bool exit = false;
	
	while (!exit)
	{
		string command = Console.ReadLine();
	
		string[] commands = command.Trim().ToLower().Split(" ");
	
		switch (commands[0])
		{
			case "add":
				Console.WriteLine(commands[1] + commands[2]);
				break;
			
			case "subtract":
				Console.WriteLine(commands[1] - commands[2]);
				break;
			
			case "multiply":
				Console.WriteLine(commands[1] * commands[2]);
				break;
			
			case "divide":
				Console.WriteLine(commands[1] / commands[2]);
				break;
			
			case "exit":
				exit = true;
				break;
		}
	}
}