#include <bits/stdc++.h>
using namespace std;
void Init();
void TypeLetter(char L);
void UndoCommands(int U);
char GetLetter(int P);
int pnt,cmd[1000005],dp[1000005];
int lift[25][1000005],ans[1000005];
void Init(){
pnt=0;
for (int i=0;i<=1000000;i++) cmd[i]=i;
}
void TypeLetter(char L){
int par=cmd[pnt];
ans[++pnt]=L;
lift[0][pnt]=par;
for (int i=1;i<=20;i++){
lift[i][pnt]=lift[i-1][lift[i-1][pnt]];
}
dp[pnt]=dp[par]+1;
}
void UndoCommands(int U){
++pnt;
cmd[pnt]=cmd[pnt-U-1];
}
char GetLetter(int P){
int x=cmd[pnt];
for (int i=20;i>=0;i--){
if (dp[lift[i][x]]>=P+1){
x=lift[i][x];
}
}
return ans[x];
}
/*int main(){
Init();
while (true){
char type,c; cin>>type>>c;
if (type=='A') TypeLetter(c);
else if (type=='B') UndoCommands(c-'0');
else cout<<GetLetter(c-'0')<<"\n";
}
}*/
