const int mxn = 1e6 + 5;
const int k = 17;
int cur = 1;
int par[mxn][k];
int val[mxn],depth[mxn];
void Init() {
depth[0] = 0;
val[0] = 0;
par[0][0] = -1;
}
void TypeLetter(char L) {
val[cur] = L - 'a';
depth[cur] = depth[cur - 1] + 1;
par[cur][0] = cur - 1;
for (int i = 1;i<k;++i){
if (depth[cur] - (1<<i) >= 0){
par[cur][i] = par[par[cur][i - 1]][i - 1];
}
}
cur++;
}
void UndoCommands(int U) {
depth[cur] = depth[cur - U - 1];
val[cur] = val[cur - U - 1];
par[cur][0] = par[cur - U - 1][0];
for (int i = 1;i<k;++i){
if (depth[cur] - (1<<i) >= 0){
par[cur][i] = par[par[cur][i - 1]][i - 1];
}
}
++cur;
}
char GetLetter(int P) {
int v = depth[cur - 1] - P;
int pos = cur - 1;
for (int i = k - 1;i>=0;--i){
if (depth[pos] - (1<<i) >= v){
pos = par[pos][i];
}
}
return char(val[pos] + 'a');
}
