#include <bits/stdc++.h>
using namespace std;
vector<int> from, depth;
vector<vector<int>> anc;
vector<char> type;
void Init() {
type.push_back(' ');
depth.push_back(0);
anc.push_back(vector<int>());
from.push_back(0);
}
void TypeLetter(char L) {
type.push_back(L);
depth.push_back(depth[from.back()] + 1);
anc.push_back(vector<int>(1, from.back()));
for (int i = 1; depth.back() >> i; ++i) {
anc.back().push_back(anc[anc.back()[i - 1]][i - 1]);
}
from.push_back(from.size());
}
void UndoCommands(int U) {
type.push_back(' ');
depth.push_back(-1);
anc.push_back(vector<int>());
from.push_back(from[from.size() - 1 - U]);
}
char GetLetter(int P) {
int jump = depth[from.back()] - 1 - P;
int x = from.back();
for (int i = 0; jump; ++i) {
if (jump >> i & 1) {
x = anc[x][i];
jump -= 1 << i;
}
}
return type[x];
}
