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

int opcodeToNum(char* opcode);

int main() {
    int N;
    scanf("%d\n",&N);
    int queue[10000];
    int front = 0, rear = 0, size = 0;

    while(N--){
        char opcode[6];
        int operend;
        scanf("%s",opcode);

        switch(opcodeToNum(opcode))
        {
            case 0:
            {
                scanf("%d\n",&operend);
                queue[rear++] = operend;
                size++;
                break;
            }
            case 1:
            {
                printf("%d\n", size ? queue[front++] : -1);
                size = size ? size - 1 : 0;
                break;
            }
            case 2:
            {
                printf("%d\n",size);
                break;
            }
            case 3:
            {
                printf("%d\n", size ? 0 : 1);
                break;
            }
            case 4:
            {
                printf("%d\n", size ? queue[front] : -1);
                break;
            }
            case 5:
            {
                printf("%d\n", size ? queue[rear-1] : -1);
            }
        }
    }
    return 0;
}

int opcodeToNum(char* opcode){
    if(!strcmp(opcode, "push")) return 0;
    else if(!strcmp(opcode, "pop")) return 1;
    else if(!strcmp(opcode, "size")) return 2;
    else if(!strcmp(opcode, "empty")) return 3;
    else if(!strcmp(opcode, "front")) return 4;
    else if(!strcmp(opcode, "back")) return 5;
    return -1;
}