statement.md

lab01-stack

Simulate a LIFO stack of integers.

Input

• Line 1: integer N — the number of operations.
• Next N lines: each is either
  • push X — push integer X onto the stack, or
  • pop — remove and report the value on top of the stack.

Output

For each pop operation, print the value removed from the top of the stack on its own line. If the stack is empty when pop is issued, print -1.

Example

Input:

5
push 3
push 7
pop
pop
pop

Output:

7
3
-1