import sys # for line in sys.stdin: # a = line.split() # print(int(a[0]) + int(a[1])) def solver(): cmd=[] arr=[] n =int(input()) for i in range(n): cmd.append(input()) for line in cmd: if "push" in line: arr.append(line.split(" ")[1] ) elif line=="pop": if len(arr)>0: ret=arr[-1] #arr=arr[:-1] # 会超时 arr.pop() # 不会超时 print(ret) else: print("error") elif line=="top": if len(arr)>0: print(arr[-1]) else: print("error") solver()