Implement a last-in-first-out stack driven by a command stream.
Implement a stack of integers. Process commands from stdin, one per line.
Commands:
- PUSH <value> : push an integer onto the top of the stack.
- POP : remove and print the top value, or print "EMPTY" if the stack is empty.
- PEEK : print the top value without removing it, or "EMPTY" if the stack is empty.
- SIZE : print the number of values currently on the stack.