#include <bits/stdc++.h>

using namespace std;

struct node {
    int key, prior, minv, maxv, ans, cnt;
    node *l, *r;
};

typedef node* pnode;

int q, a, b;
char c;

int cnt(pnode t) {
    return t ? t->cnt : 0;
}

int choose(int A, int B) {
    if (A == -1) return B;
    if (B == -1) return A;
    return min(A, B);
}

void updnd(pnode t) {
    if (!t) return;
    t->cnt = 1 + cnt(t->l) + cnt(t->r);
    if (t->l && t->r) {
        t->ans = choose(t->l->ans, t->r->ans);
        int V = min(t->r->minv - t->key, t->key - t->l->maxv);
        t->ans = choose(V, t->ans);
        t->maxv = max(t->key, max(t->r->maxv, t->l->maxv));
        t->minv = min(t->key, min(t->r->minv, t->l->minv));
    } else if (!t->l && !t->r) {
        t->ans = -1, t->minv = t->maxv = t->key;
    } else {
        pnode oquepresta = t->l ? t->l : t->r;
        int V = min(abs(oquepresta->minv - t->key), abs(oquepresta->maxv - t->key));
        t->ans = choose(V, choose(t->ans, oquepresta->ans));
        t->maxv = max(t->key, oquepresta->maxv);
        t->minv = min(t->key, oquepresta->minv);
    }
}

pnode newnode(int v=0) {
    pnode t = (pnode)malloc(sizeof(node));
    t->l = t->r = nullptr;
    t->prior = rand();
    t->key = v;
    t->minv = t->maxv = v;
    t->ans = -1;
    t->cnt = 1;
    return t;
}
// <=k -> u
void split(pnode t, pnode &u, pnode &v, int k) {
    if (!t) return void(u = v = nullptr);
    if (t->key <= k) split(t->r, t->r, v, k), u=t;
    else split(t->l, u, t->l, k), v=t;
    updnd(t);
}

void merge(pnode &t, pnode u, pnode v) {
    if (!u || !v) t = u ? u : v;
    else if (u->prior > v->prior) merge(u->r, u->r, v), t=u;
    else merge(v->l, u, v->l), t=v;
    updnd(t);
}

void insert(pnode &t, pnode it) {
    if (!t) return void(t = it);
    if (t->prior > it->prior)
        insert(t->key > it->key ? t->l : t->r, it);
    else
        split(t, it->l, it->r, it->key), t=it;
    updnd(t);
}

bool exists(pnode &t, pnode it) {
    if (!t) return false;
    if (t->key == it->key) return true;
    else if (t->key > it->key) return exists(t->r, it);
    else return exists(t->l, it);
}

void del(pnode &t, pnode it) {
    pnode p1, p2, p3;
    split(t, p1, p2, it->key-1);
    split(p2, p2, p3, it->key);
    merge(t, p1, p3);
}

int getval(pnode t, int ind, int ac =0) {
    if (!t) return -1;
    int cur_pos = ac + cnt(t->l);
    if (cur_pos == ind) return t->key;
    else if (cur_pos > ind) return getval(t->l, ind, ac);
    else return getval(t->r, ind, cur_pos+1);
}

int query(pnode t, int a, int b, int ac=0) {
    int i1 = getval(t, a), i2 = getval(t, b);
    cerr << i1 << " " << i2 << "\n";
    pnode p1, p2, p3;
    split(t, p1, p2, i1-1);
    split(p2, p2, p3, i2);
    int answer = p2->ans;
    merge(p2, p2, p3);
    merge(t, p1, p2);
    return answer;
}

int main() {
    cin >> q;
    pnode T = newnode(-10);
    for (int i = 1; i <= q; i++) {
        cin >> c;
        if (c == 'I') {
            cin >> a;
            pnode nn = newnode(a);
            if (!exists(T, nn)) insert(T, nn);
        } else if (c == 'D') {
            cin >> a;
            pnode nn = newnode(a);
            if (!exists(T, nn)) del(T, nn);
        } else if (c == 'N') {
            cin >> a >> b;
            if (b == a) cout << "-1\n";
            else cout << query(T, a+1, b+1) << "\n";
        } else {
            cin >> a >> b;
            if (b == a) cout << "-1\n";
            else cout << getval(T, b+1) - getval(T, a+1) << "\n";
        }
    }
}