#include <bits/stdc++.h>
#define Loop(x,l,r) for (ll x = (l); x < (r); ++x)
#define LoopR(x,l,r) for (ll x = (r)-1; x >= (l); --x)
typedef long long ll;
typedef std::pair<int, int> pii;
typedef std::pair<ll , ll > pll;
using namespace std;
const int lg = 20;
struct node {
int par_com[lg];
int par_let[lg];
int len;
char let;
};
int cur;
node pool[250'000'000/sizeof(node)];
int next_node = 0;
int new_node()
{
return next_node++;
}
void Init()
{
cur = new_node();
Loop (i,0,lg) {
pool[cur].par_com[i] = cur;
pool[cur].par_let[i] = cur;
}
pool[cur].len = 0;
pool[cur].let = 0;
}
void calc_par_com(int t)
{
if (pool[t].par_com[1] != -1)
return;
calc_par_com(pool[t].par_com[0]);
Loop (i,0,lg-1) {
pool[t].par_com[i+1] = pool[pool[t].par_com[i]].par_com[i];
}
}
static void calc_par_let(int t)
{
if (pool[t].par_let[1] != -1)
return;
calc_par_let(pool[t].par_let[0]);
Loop (i,0,lg-1) {
pool[t].par_let[i+1] = pool[pool[t].par_let[i]].par_let[i];
}
}
void TypeLetter(char L)
{
int next = new_node();
pool[next].par_com[0] = cur;
pool[next].par_let[0] = cur;
pool[next].par_com[1] = -1;
pool[next].par_let[1] = -1;
pool[next].len = pool[pool[next].par_let[0]].len + 1;
pool[next].let = L;
cur = next;
}
void UndoCommands(int U)
{
int sib = cur;
calc_par_com(cur);
Loop (i,0,lg) {
if (U & (1<<i))
sib = pool[sib].par_com[i];
}
int next = new_node();
pool[next].par_com[0] = cur;
pool[next].par_let[0] = pool[sib].par_let[0];
pool[next].par_com[1] = -1;
pool[next].par_let[1] = -1;
pool[next].len = pool[pool[next].par_let[0]].len + 1;
pool[next].let = pool[sib].let;
cur = next;
}
char GetLetter(int P)
{
P = pool[cur].len - 1 - P;
int ans = cur;
calc_par_let(cur);
Loop (i,0,lg) {
if (P & (1<<i))
ans = pool[ans].par_let[i];
}
return pool[ans].let;
}
