#include <vector>
#include <iostream>
using namespace std;
const int mx = 1'000'000;
const int lg_mx = 20;
int curr;
int len[1+mx];
char last[1+mx];
int letter_anc[1+mx][lg_mx];
int undo_anc[1+mx][lg_mx];
int lg2[1+mx];
void Init()
{
lg2[0] = -1;
lg2[1] = 0;
for(int i = 2; i <= mx; i++)
lg2[i] = lg2[i/2] + 1;
curr = 0;
len[0] = -1;
last[0] = '?';
for(int e = 0; e < lg_mx; e++)
letter_anc[0][e] = undo_anc[0][e] = 0;
}
void TypeLetter(char L)
{
curr++;
len[curr] = len[curr-1] + 1;
last[curr] = L;
letter_anc[curr][0] = curr-1;
undo_anc[curr][0] = curr-1;
for(int e = 1; e < max(lg2[curr], lg2[len[curr]])+2; e++)
{
letter_anc[curr][e] = letter_anc[ letter_anc[curr][e-1] ][e-1];
undo_anc[curr][e] = undo_anc[ undo_anc[curr][e-1] ][e-1];
}
// cerr << curr << '\n';
}
void UndoCommands(int U)
{
int prev = curr;
for(int e = 0; e < lg2[curr]+2; e++)
{
if(U & (1 << e))
prev = undo_anc[prev][e];
}
// cerr << "making copy of " << prev << '\n';
curr++;
len[curr] = len[prev];
last[curr] = last[prev];
letter_anc[curr][0] = letter_anc[prev][0];
undo_anc[curr][0] = curr-1;
for(int e = 1; e < max(lg2[curr], lg2[len[curr]])+2; e++)
{
letter_anc[curr][e] = letter_anc[ letter_anc[curr][e-1] ][e-1];
undo_anc[curr][e] = undo_anc[ undo_anc[curr][e-1] ][e-1];
}
// cerr << curr << '\n';
}
char GetLetter(int P)
{
int pos = curr;
for(int e = max(lg2[curr], lg2[len[curr]])+2; e >= 0; e--)
if(len[ letter_anc[pos][e] ] >= P)
pos = letter_anc[pos][e];
return last[pos];
}
