#include"bits/stdc++.h"
//#include"scrivener.h"
#define overload(a,b,c,d,...) d
#define rep1(a) for(ll _=0;_<(ll)a;++_)
#define rep2(i,a) for(ll i=0;i<(ll)(a);++i)
#define rep3(i,a,b) for(ll i=(ll)(a);i<(ll)(b);++i)
#define rep(...) overload(__VA_ARGS__,rep3,rep2,rep1)(__VA_ARGS__)
#define rrep1(i,a) for(ll i=(ll)(a)-1;i>=0;--i)
#define rrep2(i,a,b) for(ll i=(ll)(b)-1;i>=(ll)(a);--i)
#define rrep(...) overload(__VA_ARGS__,rrep2,rrep1)(__VA_ARGS__)
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
#define pb push_back
#define eb emplace_back
using namespace std;
using ll=long long;
using ull=unsigned long long;
using i128=__int128_t;
using ld=long double;
using vi=vector<int>;
using vl=vector<ll>;
template<typename T,typename U>inline bool chmin(T&a,const U&b){return (a>b?a=b,true:false);}
template<typename T,typename U>inline bool chmax(T&a,const U&b){return (a<b?a=b,true:false);}
struct Node{
int val;
int ch[2]={};
Node():val(-1){
ch[0]=ch[1]=-1;
}
};
Node nodes[10000000];
int sz;
void destructive_set(Node&nd,int idx,int val){
if(idx==0)nd.val=val;
if(nd.ch[idx&1]==-1)nd.ch[idx&1]=sz,nodes[sz++]=Node();
else destructive_set(nodes[nd.ch[idx&1]],idx>>1,val);
}
void build(const vector<int>&a){
for(int i=0;i<(int)a.size();++i){
destructive_set(nodes[0],i,a[i]);
}
}
int change(const Node&nd,int idx,int val){
int res=sz;
Node&ret=nodes[sz++];
nodes[sz-1]=Node();
ret.ch[0]=nd.ch[0],ret.ch[1]=nd.ch[1];
if(idx==0){
ret.val=val;
}
else{
if(ret.ch[idx&1]==-1){
ret.ch[idx&1]=sz;
nodes[sz++]=Node();
}
ret.ch[idx&1]=change(nodes[ret.ch[idx&1]],idx>>1,val);
}
return res;
}
int get(const Node&nd,int idx){
if(idx==0)return nd.val;
if(nd.ch[idx&1]==-1)return -1;
return get(nodes[nd.ch[idx&1]],idx>>1);
}
vector<pair<int,Node>>st;
void Init() {
st.clear();
sz=1;
nodes[0]=Node();
st.eb(0,nodes[0]);
}
void TypeLetter(char L) {
//cerr<<"Type Letter "<<L<<endl;
int len=st.back().first;
Node&nd=st.back().second;
st.emplace_back(len+1,nodes[change(nd,len,L-'a')]);
//cerr<<sz<<endl;
}
void UndoCommands(int U) {
//cerr<<"Undo Commands "<<U<<endl;
assert(st.size()>=U);
st.emplace_back(st[st.size()-1-U]);
//cerr<<sz<<endl;
}
char GetLetter(int P) {
//cerr<<"Get Letter "<<P<<endl;
return 'a'+get(st.back().second,P);
}
