import sys
from collections import deque
input = sys.stdin.readline
Q = int(input())
stack = deque()
persistent_stack = deque()
for _ in range(Q):
query = list(map(int, input().split()))
query_type = query[0]
if query_type == 1:
i = query[1]
stack.append(i)
persistent_stack.append((i, 0))
elif query_type == 2:
i = stack.pop()
persistent_stack.append((i, 1))
elif query_type == 3:
j = query[1]
for _ in range(j):
v, t = persistent_stack.pop()
if t:
stack.append(v)
else:
stack.pop()
elif query_type == 4:
print(len(stack))
elif query_type == 5:
if not stack:
print(-1)
else:
print(stack[-1])
