#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;
}