#include <stdio.h>
#include <string.h>
int main() {
    int dq[1000], f = 0, r = -1;
    int main() {
        int n,x;
        char cmd[20];
    scanf("%d", &n);
    while (n--) {
        scanf("%s", cmd);
        if (!strcmp(cmd,"priority_board")){
            int x; scanf("%d", &x);
            dq[++r] = dq[f];
            dq[f] = x;
        }
        else if (!strcmp(cmd, "general_board")) {
            int x; scanf("%d", &x);
            dq[++r] = x;
        }
        else if (!strcmp(cmd,"board_train")) {
            if (f > r) printf("Invalid operation\n");
            else f++;
        }
        else if (!strcmp(cmd, "display"))
{
            if (f > r) printf("No passenger\n");
            else {
                for (int i = f; i <= r; i++)
                printf("%d ",dq[i]);
                printf("\n");
            }
        }
    }
    return 0;
}