struct TYPE{
char num;
int next_0, lev, next[21];
} d[1000001];
int n, p[21];
void Init(){
p[0] = 1;
for (int i = 1; i <= 20; i++) p[i] = p[i - 1] * 2;
}
void TypeLetter(char x){
n++, d[n].next_0 = n, d[n].num = x, d[n].lev = d[n - 1].lev + 1;
d[n].next[0] = d[n - 1].next_0;
for (int i = 1; i <= 20; i++) d[n].next[i] = d[d[n].next[i - 1]].next[i - 1];
}
void UndoCommands(int x) {
n++, d[n].next_0 = d[n - x - 1].next_0, d[n].lev = d[d[n].next_0].lev;
}
char GetLetter(int _in){
int x = n, y = d[n].lev-_in-1;
while(1){
if(x!=d[x].next_0) x=d[x].next_0;
else if(y==0) return d[x].num;
for(int i=20; i>=0; i--)
if(p[i]<=y){
x=d[x].next[i], y-=p[i];
break;
}
}
}
