import sys N = int(input()) stack = [] for _ in range(N): line = sys.stdin.readline().split() if line[0] == "push": stack.append(int(line[1])) elif line[0] == "pop": if len(stack)>0: print(stack[-1]) stack.pop() else: print(-1) elif line[0] == "size": print(len(stack)) elif line[0] == "empty": if len(stack) == 0: print(1) else: print(0) elif line[0] == "top": if len(stack) > 0: print(stack[-1]) ..