#include <bits/stdc++.h>
//#pragma GCC optimize ("O2,unroll-loops")
//#pragma GCC optimize("no-stack-protector,fast-math")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<pii, int> piii;
typedef pair<ll, ll> pll;
#define debug(x) cerr<<#x<<'='<<(x)<<endl;
#define debugp(x) cerr<<#x<<"= {"<<(x.first)<<", "<<(x.second)<<"}"<<endl;
#define debug2(x, y) cerr<<"{"<<#x<<", "<<#y<<"} = {"<<(x)<<", "<<(y)<<"}"<<endl;
#define debugv(v) {cerr<<#v<<" : ";for (auto x:v) cerr<<x<<' ';cerr<<endl;}
#define all(x) x.begin(), x.end()
#define pb push_back
#define kill(x) return cout<<x<<'\n', 0;
const int inf=1000000010;
const ll INF=1000000000000001000LL;
const int mod=1000000007;
const int MAXN=1000010, LOG=20;
int n, m, k, u, v, x, y, t, a, b, ans;
int par[MAXN][LOG], sz[MAXN];
char last[MAXN];
void Init(){
}
void TypeLetter(char ch){
par[n+1][0]=n;
sz[n+1]=sz[n]+1;
last[n+1]=ch;
n++;
if (!last[par[n][0]]) par[n][0]=par[par[n][0]][0];
for (int i=1; i<LOG; i++) par[n][i]=par[par[n][i-1]][i-1];
}
void UndoCommands(int ted){
par[n+1][0]=n-ted;
n++;
if (!last[par[n][0]]) par[n][0]=par[par[n][0]][0];
sz[n]=sz[par[n][0]];
for (int i=1; i<LOG; i++) par[n][i]=par[par[n][i-1]][i-1];
}
char GetLetter(int pos){
int v=n;
for (int i=LOG-1; ~i; i--) if (sz[par[v][i]]>pos) v=par[v][i];
return last[v];
}
