#include <vector>
#include <algorithm>
#include <set>
#define ad push_back
using namespace std;
const int N = 1e6 + 10;
int a[N], i1 = 1;
int p[N][20];
char c[N];
vector<int> fp;
void Init()
{
fp.ad(0);
}
void TypeLetter(char L)
{
a[i1] = a[i1 - 1] + 1;
c[i1] = L;
i1++;
}
void UndoCommands(int U)
{
a[i1] = a[i1 - U - 1];
fp.ad(i1);
p[i1][0] = *(--lower_bound(fp.begin(), fp.end(), i1 - U));
for (int i = 1; i < 20; i++) p[i1][i] = p[p[i1][i - 1]][i - 1];
i1++;
}
char GetLetter(int P)
{
P++;
int s = fp.back();
for (int i = 20 - 1; i >= 0; i--)
if (a[p[s][i]] >= P)s = p[s][i];
if (a[s] >= P) s = p[s][0];
s += P - a[s];
return c[s];
}
