#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int opcodeToNum(char* opcode){
    if(!strcmp(opcode, "push")) return 0;
    if(!strcmp(opcode, "pop")) return 1;
    if(!strcmp(opcode, "size")) return 2;
    if(!strcmp(opcode, "empty")) return 3;
    if(!strcmp(opcode, "top")) return 4;
    return -1;
}

int main() {
    int N;
    scanf("%d",&N);
    int* stack = (int*)malloc(sizeof(int)* N);
    memset(stack,0,sizeof(int)*N);

    int len = 0;
    while(N--){
        char str[13];
        if (fgets(str, sizeof(str), stdin) == NULL) break;
        if (str[0] == '\n') { N++; continue; }
        str[strcspn(str, "\n")] = 0;
        char *opcode = strtok(str, " ");
        char *operend = strtok(NULL, " ");
        int opNum = opcodeToNum(opcode);
        int operendNum = operend ? atoi(operend) : 0;
        
        switch (opNum)
        {
        case 0:
            stack[len] = operendNum;
            len++;
            break;
        case 1:
            if(len==0) {
                printf("-1\n");
            }
            else {
                printf("%d\n",stack[--len]);
            }
            break;
        case 2:
            printf("%d\n",len);
            break;
        case 3:
            printf("%d\n", len ? 0 : 1);
            break;
        case 4:
            printf("%d\n", len ? stack[len-1] : -1);
            break;
        }
    }

    free(stack);
    return 0;
}