N=int(input())
stack = []
for _ in range(N):
    a= input().split()
    if a[0] == '1':
        stack.append(a[1])
        
    elif a[0] == '2':
        if stack == []:
            print(-1)
        else:
            print(stack.pop())
            
    elif a[0] == '3':
        print(len(stack))

    elif a[0] == '4':
        if stack == []:
            print(1)
        else:
            print(0)

    elif a[0] == '5':
        if stack !=[]:
            print(stack[-1])
        else:
            print(-1)