#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;
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];
}
