#include<bits/stdc++.h>
using namespace std;
struct node
{
    long long v, p, s;
    node *l, *r;
    node()
    {
        l = r = NULL;
        v = p = 0;
        s = 0;
    }
};
typedef long long int ll;
typedef node* pnode;
ll n, q;
char c;
ll sz(pnode t)
{
    if (t)return t->s;
    return 0;
}
void upsz(pnode &t)
{
    if (!t)return;
    t->s = sz(t->r) + sz(t->l) + 1;
}
void split(pnode t, pnode &l, pnode &r,ll k)
{
    if (!t)l = r = NULL;
    else if (t->v <= k)split(t->r,t->r,r,k),l = t;
    else split(t->l, l, t->l, k), r = t;
    upsz(t);
}
void merge(pnode &t, pnode l, pnode r)
{
    if (!l)t = r;
    else if (!r)t = l;
    else if (l->p > r->p)merge(l->r,l->r, r), t = l;
    else merge(r->l, l, r->l), t = r;
    upsz(t);
}
void ins(pnode nt, pnode &t)
{
    if (!t || !(t->s))t = nt;
    else if (t->p < nt->p)split(t, nt->l, nt->r, nt->v), t = nt;
    else if (nt->v <= t->v)ins(nt, t->l);
    else ins(nt, t->r);
    upsz(t);
}
void era(pnode &t, ll k)
{
    if (!t)return;
    else if (t->v == k){ pnode te = t; merge(t, t->l, t->r); te = NULL; }
    else if (t->v > k)era(t->l, k);
    else era(t->r, k);
    upsz(t);
}
bool find(pnode t,ll va)
{
    if (!t || t->s==0)return false;
    if (t->v == va)return 1;
    if (t->v > va)return find(t->l,va);
    else return find(t->r, va);
}
pnode ne(ll va)
{
    pnode r=new node();
    r->l = r->r = NULL;
    r->s = 1;
    r->v = va;
    r->p = rand();
    return r;
}
ll kth(pnode &t, ll k,ll l)
{
    if (l + sz(t->l)+1== k)
        return t->v;
    else if (k > l + sz(t->l))
        return kth(t->r, k, l + sz(t->l)+1);
    else
        return kth(t->l,k,l);
}
ll co(pnode &t,ll x)
{
    if (!t)return 0;
    if (t->v == x)return sz(t->l);
    if (t->v < x)return sz(t->l) + 1 + co(t->r, x);
    return co(t->l, x);
}
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    pnode t = new node();
    cin >> q;
    while (q--)
    {
        cin >> c >> n;
        if (c == 'I')
        {
            if (find(t, n))
                continue;
            ins(ne(n), t);
        }
        else if (c == 'D')
            era(t, n);
        else if (c == 'K')
        {
            if (t->s < n)cout << "invalid";
            else cout << kth(t, n,0);
            cout << "\n";
        }
        else
            cout << co(t, n) << "\n";
    }
    return 0;
}