//In the name of God
#include <bits/stdc++.h>
using namespace std;
typedef int ll;
typedef pair<ll, ll> pll;
const ll maxn = 1e6 + 100;
const ll lg = 21;
const ll mod = 1e9 + 7;
const ll inf = 1e9;
#define fast_io ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define file_io freopen("input.txt", "r+", stdin);freopen("output.txt", "w+", stdout);
#define pb push_back
#define Mp make_pair
#define F first
#define S second
#define Sz(x) ll((x).size())
#define all(x) (x).begin(), (x).end()
ll pos[maxn], g[maxn][26], t, c, h[maxn], p[maxn][lg];
char ch[maxn];
void Init(){
}
void TypeLetter(char L){
ll x = ll(L - 'a');
ll v = pos[c];
if(!g[v][x]){
g[v][x] = ++t;
p[t][0] = v;
h[t] = h[v] + 1;
ch[t] = L;
for(ll i = 1; i < lg; i++){
p[t][i] = p[p[t][i - 1]][i - 1];
}
}
pos[++c] = g[v][x];
return;
}
void UndoCommands(int U){
pos[c + 1] = pos[c - U];
c++;
return;
}
ll par(ll x, ll y){
for(ll i = 0; i < lg; i++){
if((y >> i) & 1) x = p[x][i];
}
return x;
}
char GetLetter(int P){
ll x = h[pos[c]] - P - 1;
return ch[par(pos[c], x)];
}
/*int main(){
fast_io;
Init();
TypeLetter('a');
TypeLetter('b');
cout << GetLetter(1);
TypeLetter('d');
UndoCommands(2);
UndoCommands(1);
cout << GetLetter(2);
TypeLetter('e');
UndoCommands(1);
UndoCommands(5);
TypeLetter('c');
cout << GetLetter(2);
UndoCommands(2);
cout << GetLetter(2);
return 0;
}*/
