Type a positive integer to push it,
non-positive to pop the stack,
control-d to halt.

Go ahead: 10
Go ahead: 20
Go ahead: 30
Go ahead: 0
30
Go ahead: 0
20
Go ahead: 40
Go ahead: 0
40
Go ahead: 0
10
Go ahead: 0
Underflow: can't take blood from a stone.
Try again.
Go ahead: The stack has already been destructed.