#include <stdio.h>
#include <stdlib.h>

#define MAX 1000000
int stack[MAX];

int main() {
    int n, a, x;
    scanf("%d", &n);

    int top = 0;
    for(int i=0; i<n; i++){
        scanf("%d", &a);

        switch(a){
            case 1:
                scanf("%d", &x);
                if(top < MAX){
                    stack[top] = x;
                    top++;
                }
                break;
            
            case 2:
                if(top <= 0){
                    printf("-1\n");
                }else{
                    printf("%d\n", stack[top - 1]);
                    top--;
                }
                break;
            
            case 3:
                printf("%d\n", top);
                break;
            
            case 4:
                if(top <= 0){
                    printf("1\n");
                }else{
                    printf("0\n");
                }
                break;

            case 5:
                if(top <= 0){
                    printf("-1\n");
                }else{
                    printf("%d\n", stack[top-1]);
                }
                break;
        }
    }
    return 0;
}