ORDSET

#include<bits/stdc++.h>
using namespace std;
/// from HUNG MINE with love <3
int t[1000001][3], cc = 1, fin[1000001], par[1000001], cnt[1000001], q, x;
const int add = 1e9;
void ins (int x) {
      int r = 1;
      for (int k = 30; k >= 0; -- k) {
            int i = ((x >> k) & 1);
            if (t[r][i] == 0) {
                  ++ cc;
                  t[r][i] = cc;
                  par[cc] = r;
            }
            r = t[r][i];
      }
      if (fin[r] == 1) return;
      fin[r] = 1;
      ++ cnt[r];
      while (r != 1) {
            r = par[r];
            ++ cnt[r];
      }
}
void del (int x) {
      int r = 1;
      for (int k = 30; k >= 0; -- k) {
            int i = (x >> k) & 1;
            if (t[r][i] == 0) return;
            r = t[r][i];
      }
      if (fin[r] == 0) return;
      fin[r] = 0;
      -- cnt[r];
      while (r != 1) {
            r = par[r];
            -- cnt[r];
      }
}
int pth (int p) {
      int r = 1;
      if (cnt[r] < p) return -1e9;
      int x = 0;
      for (int k = 30; k >= 0; -- k) {
            int i = t[r][0];
            if (p > cnt[i]) {
                  x |= (1 << k);
                  p -= cnt[i];
                  r = t[r][1];
            }
            else {
                  r = t[r][0];
            }
      }
      return x;
}
int cou (int x) {
      int r = 1;
      int res = 0;
      for (int k = 30; k >= 0; -- k) {
            int i = ((x >> k) & 1);
            if (i == 1) res += cnt[t[r][0]];
            if (t[r][i] == 0) return res;
            r = t[r][i];
      }
      return res;
}
int main () {
      if (fopen ("test.inp", "r")) {
            freopen ("test.inp", "r", stdin);
      }
//      else {
//            freopen ("ORDSET.inp", "r", stdin);
//            freopen ("ORDSET.out", "w", stdout);
//      }

      ios_base :: sync_with_stdio (0);
      cin.tie (0);
      cout.tie (0);
      cin >> q;
      while (q --) {
            char c;
            cin >> c;
            if (c == 'I') {
                  cin >> x;
                  ins (x + add);
            }
            else if (c == 'D') {
                  cin >> x;
                  del (x + add);
            }
            else if (c == 'K') {
                  cin >> x;
                  if (pth (x) == -1e9) {
                        cout << "invalid\n";
                  }
                  else {
                        cout << pth (x) - add<< "\n";
                  }
            }
            else {
                  cin >> x;
                  cout << cou (x + add) << "\n";
            }
      }
}