#include <bits/stdc++.h>
using namespace std;
const int LOG = 21;
struct node
{
char c; int s;
node *anc[LOG];
node(){
for(int i=0;i<LOG;i++) anc[i] = NULL;
s=0;
}
}*tree [1000005];
int id;
void Init(){
id=1;
tree[0] = new node();
}
void TypeLetter(char L) {
int n=id++;
tree[n] = new node();
tree[n]->s = tree[n-1]->s+1;
tree[n]->c = L;
tree[n]->anc[0]=tree[n-1];
for(int i=1;i<LOG;i++) tree[n]->anc[i] = (tree[n]->anc[i-1]) ? (tree[n]->anc[i-1])->anc[i-1] : NULL;
}
void UndoCommands(int U) {
int ret=id-1-U;
int n=id++;
tree[n]=tree[ret];
}
char GetLetter(int P) {
int n=id-1;
node *h = new node();
h=tree[n];
int up=tree[n]->s - 1 - P;
for(int i=LOG-1;i>=0;i--){
if(up - (1<<i) >= 0){
up-=(1<<i);
h=h->anc[i];
}
}
return h->c;
}
