[백준 10828] 스택

import sys

stack=[]
n=int(sys.stdin.readline().rstrip())
for i in range(n):
    command=sys.stdin.readline().rstrip()
    if command[:2]=='pu':
        stack.append(int(command[5:]))
    if command[:2]=='to':
        if len(stack)==0:
            print(-1)
        else :
            print(stack[len(stack)-1])
    if command[:2]=='si':
        print(len(stack))
    if command[:2]=='po':
        if len(stack)==0:
            print(-1)
        else :
            print(stack.pop())
    if command[:2]=='em':
        if len(stack)==0:
            print(1)
        else :
            print(0)

 

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