#include <bits/stdc++.h>
using namespace std;
 
typedef long long ll;
#define FOR(i,N) for(ll i = 0; i < N; i++)
#define all(x) (x).begin(), (x).end()
#define F first
#define S second
vector<int> cmd = {0};  // cmd[i] -> idx of cur node    after ith command (1-indexed)
vector<int> len = {0};  // len[i] -> len of cur string  after ith command (1-indexed)
vector<char> node; // node value
vector<vector<int>> par(2e6, vector<int>(20)); // node parent (binary jumping)
int n = 0; // nodes created
void Init() {}
void TypeLetter(char ch) {
    len.push_back(len[cmd.back()] + 1);
    par[n][0] = cmd.back();
    cmd.push_back(n);
    node.push_back(ch);
    for(int j = 1; j < 20; j++) par[n][j] = par[par[n][j-1]][j-1];
    n++;
}
void UndoCommands(int k) {
    cmd.push_back(cmd[cmd.size()-1-k]);
}
char GetLetter(int k) {
    k = k - len[cmd.back() + 1] - 1;
    int j = 19;
    int bru = cmd.back();
    while(j > -1) {
        if (pow(2, j) <= k) {
            bru = par[bru][j];
            k -= pow(2, j);
        }
        j--;
    }
    return node[bru];
}
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