main.py

# Authored by : tony9402
# Co-authored by : -
# Link : http://boj.kr/ab416f0794fc41cabc3d9ed46db29f60
import sys

def input():
    return sys.stdin.readline().rstrip()

N = int(input())

stack = [] 

for i in range(N):
    cmd = input().split()
    X = 0
    if len(cmd) == 2:
        X = cmd[1]
    cmd = cmd[0]

    if cmd == "push":
        stack.append(X)
    elif cmd == "pop":
        if len(stack) == 0:
            print(-1)
        else:
            print(stack[-1])
            stack.pop(-1)
    elif cmd == "size":
        print(len(stack))
    elif cmd == "empty":
        print(0 if len(stack) else 1)
    elif cmd == "top":
        if len(stack) == 0:
            print(-1)
        else:
            print(stack[-1])