[백준] 28278 스택2

import sys

n = int(sys.stdin.readline())
stack = []
for i in range(n):
    data = list(map(int,sys.stdin.readline().split()))
    if data[0] == 1:
        stack.append(data[1])

    if data[0] == 2:
        print(-1 if len(stack)==0 else stack.pop())

    if data[0] == 3:
        print(len(stack))

    if data[0] == 4:
        print(1 if len(stack)==0 else 0)

    if data[0] == 5:
        print(-1 if len(stack) == 0 else stack[-1])