#include <iostream> using std::cin; using std::cout; using std::endl; // Limits const int N = 100005; // Variables int n; char op; // Persistent Segment Tree int p, cnt, root[N]; int insert(int, int, int, int); int query(int, int, int, int); int main() { cin >> n; for (int i = 1; i <= n; i++) { cin >> op; if (op == 'T') { char x; cin >> x; int k = x - 'a'; root[p + 1] = insert(root[p], 1, n, k); p++; } else if (op == 'U') { int x; cin >> x; root[p + 1] = root[std::max(p - x, 0)]; p++; } else { int x; cin >> x; cout << char(query(root[p], 1, n, x) + 'a') << endl; } } return 0; } // Persistent Segment Tree struct node { int l, r, s, d; node() : l(0), r(0), s(0), d(0) {} node(int _l, int _r) : l(_l), r(_r), s(0), d(0) {} } tr[N << 5]; int insert(int p, int l, int r, int x) { int q = ++cnt; tr[q] = tr[p]; if (l == r) { tr[q].s = 1; tr[q].d = x; return q; } int mid = l + r >> 1; if (tr[tr[q].l].s < mid - l + 1) { tr[q].l = insert(tr[q].l, l, mid, x); } else { tr[q].r = insert(tr[q].r, mid + 1, r, x); } tr[q].s = tr[tr[q].l].s + tr[tr[q].r].s; return q; } int query(int p, int l, int r, int x) { if (l == r) return tr[p].d; int mid = l + r >> 1; if (x <= mid) return query(tr[p].l, l, mid, x); return query(tr[p].r, mid + 1, r, x); }