URAL 1992

#include <cstdio>
#include <iostream>
#define N 500005
using namespace std;
int now[N],tot_ro,c,p;
int stack[N],pre[N],tot;
int stack_ne[N],now_ne[N],next[N],tot_ne;
char order[100];
int main()
{
    int n,m;
    while(scanf("%d%d",&n,&m)!=EOF){
        tot=tot_ne=0;
        tot_ro=1;
        now[1]=now_ne[1]=0;
        for(int i=0; i<n; i++){
            scanf("%s",order);
            switch (order[4]) {
                case ‘n‘://learn
                    scanf("%d%d",&c,&p);
                    stack[++tot]=p;
                    pre[tot]=now[c];
                    now[c]=tot;
                    now_ne[c]=0;
                    break;
                case ‘b‘://rollback
                    scanf("%d",&c);
                    if(now[c]!=0){
                        stack_ne[++tot_ne]=stack[now[c]];
                        next[tot_ne]=now_ne[c];
                        now_ne[c]=tot_ne;
                        now[c]=pre[now[c]];
                    }
                    break;
                case ‘a‘://relearn
                    scanf("%d",&c);
                    if(now_ne[c]!=0){
                        stack[++tot]=stack_ne[now_ne[c]];
                        pre[tot]=now[c];
                        now[c]=tot;
                        now_ne[c]=next[now_ne[c]];
                    }
                    break;
                case ‘e‘://clone
                    scanf("%d",&c);
                    if(c<=tot_ro){
                        now[++tot_ro]=now[c];
                        now_ne[tot_ro]=now_ne[c];
                    }
                    break;
                case ‘k‘://check
                    scanf("%d",&c);
                    if(now[c]==0)
                        printf("basic\n");
                    else 
                        printf("%d\n",stack[now[c]]);
                    break;
            }
        }
    }
    return 0;
}