import sys

input = lambda: sys.stdin.readline().strip()
n = int(input())
arr = []
chang = 0


def push(x):
    global arr
    global chang
    arr.append(x)
    chang += 1


def pop():
    global arr
    global chang
    if chang > 0:
        x=arr.pop()
        chang -= 1
        print(x)
    else:
        print("error")


def top(chang, arr):
    if chang == 0:
        print("error")
    else:
        print(arr[-1])


for i in range(n):
    a = list(map(str, input()))
    x=len(a)
    if x==3:
        if a[0]=="p":
            pop()
        else:
            top(chang,arr)
    else:
        y=int(''.join(map(str,a[5:])))
        push(y)