n = int(input(''))
arr = []
while n>0:
    
    com = input('').split(' ')
    
    if len(com) >1: # 插入
        arr.append(int(com[1]))
    if len(com) == 1:
            if not arr:
                print('error')
                
            elif com[0] == 'pop':
                print(arr.pop())
            elif com[0] == 'top':
                print(arr[-1])      
    n -= 1