#include <stdio.h>

#include <stdlib.h>

#include<string.h>

#include<malloc.h>

// 栈结构的定义

typedef struct _stack {

	int size;   // 栈存储空间的尺寸

	int* base;   // 栈基址

	int* sp;    // 栈顶

} stack;

void init(stack* s, int n) {

	s->base = (int*)malloc(sizeof(int)*n);

	s->size = n;

	s->sp = s->base;

}

void push(stack* s, int val) {

	if(s->sp - s->base == s->size) {

		puts("none");

		exit(1);

	}

	*s->sp++ = val;

}

int pop(stack* s) {

	if(s->sp == s->base) {

		puts("none");

		exit(2);

	}

	return *--s->sp;

}

int peek(stack*s) {

	if(s->sp == s->base) {

		puts("none");

		exit(2);

	}

	return *(s->sp-1);

}

int empty(stack* s) {

	return s->sp == s->base;

}

void clean(stack* s) {

	if(s->base)

		free(s->base);

}

int main(void) {

	stack s;

	int i,n;

	int num;

	char str[30];

	init(&s, 1000);

	while(1) {

		scanf("%s",str);

		if(strcmp(str,"push")==0) {

			scanf("%d",&num);

			push(&s, num);

		} else if(strcmp(str,"top")==0) {

			printf("%d\n", peek(&s));

		} else if(strcmp(str,"pop")==0) {

			printf("%d\n", pop(&s));

		} else if(strcmp(str,"clear")==0) {

			empty(&s);

		} else if(strcmp(str,"exit")==0) {

			clean(&s);

			break;

		}

	}

	return 0;

}