#include <bits/stdc++.h>
using namespace std;
map<int,char> arr;
int len[1000001];
int mp[1000001];
int op = 0 , root = 0 , node = 0;
int lift[1000001][20];
void Init(){
mp[op] = root;
}
void TypeLetter(char l){
node++;
lift[node][0] = root;
for(int i = 1;i<20;i++){
lift[node][i] = lift[lift[node][i-1]][i-1];
}
len[node] = len[root]+1;
root = node;
op++;
mp[op] = root;
arr[root] = l;
}
void UndoCommands(int u){
mp[op+1] = mp[op-u];
root = mp[++op];
}
char GetLetter(int p){
int cc = root;
p = len[root]-(p+1);
for(int i = 19;i>=0;i--){
if(p>=(1<<i)){
p-=(1<<i);
cc =lift[cc][i];
}
}
return arr[cc];
}/*
int main(){
ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
Init();
TypeLetter('a');
cout<<root<<"\n";
TypeLetter('b');
cout<<root<<"\n";
cout<<GetLetter(1)<<"\n";
TypeLetter('d');
cout<<root<<"\n";
UndoCommands(2);
cout<<root<<"\n";
UndoCommands(1);
cout<<root<<"\n";
cout<<GetLetter(2)<<"\n";
TypeLetter('e');
UndoCommands(1);
UndoCommands(5);
TypeLetter('c');
cout<<GetLetter(2)<<"\n";
UndoCommands(2);
cout<<GetLetter(2)<<"\n";
}
*/
