#include<bits/stdc++.h>
#define int long long
using namespace std;

mt19937 gen(chrono::steady_clock::now().time_since_epoch().count());

struct node {
  int x = 0, y = gen();
  node *l = nullptr;
  node *r = nullptr;
  node() = default;
  node(int& x) {
    this->x = x;
  }
};

node* merge(node* a, node* b) {
  if (a == nullptr)
    return b;
  if (b == nullptr)
    return a;
  if (a->y > b->y) {
    a->r = merge(a->r, b);
    return a;
  } else {
    b->l = merge(a, b->l);
    return b;
  }
}

pair<node*, node*> split(node* a, int x) {
  if (a == nullptr)
    return {nullptr, nullptr};
  if (a->x < x) {
    auto spl_R = split(a->r, x);
    a->r = spl_R.first;
    return {a, spl_R.second};
  } else {
    auto spl_L = split(a->l, x);
    a->l = spl_L.second;
    return {spl_L.first, a};
  }
}

node* find(node* a, int x) {
  if (a == nullptr)
    return nullptr;
  if (a->x == x)
    return a;
  if (a->x > x)
    return find(a->l, x);
  if (a->x < x)
    return find(a->r, x);
  return nullptr;
}

node* insert(node* a, int x) {
  if (find(a, x) != nullptr)
    return a;
  node* A = new node(x);
  auto spl = split(a, x);
  A = merge(spl.first, A);
  A = merge(A, spl.second);
  return A;
}

node* erase(node* a, int x) {
  auto spl = split(a, x);
  auto spl_L = split(spl.second, x + 1);
  a = merge(spl.first, spl_L.second);
  return a;
}

node* getRight(node* a) {
  if (a == nullptr)
    return nullptr;
  return (a->r == nullptr ? a : getRight(a->r));
}

node* getLeft(node* a) {
  if (a == nullptr)
    return nullptr;
  return (a->l == nullptr ? a : getLeft(a->l));
}

node* next(node* a, int x) {
  auto spl = split(a, x + 1);
  auto ans = getLeft(spl.second);
  a = merge(spl.first, spl.second);
  return ans;
}

node* prev(node* a, int x) {
  auto spl = split(a, x);
  auto ans = getRight(spl.first);
  a = merge(spl.first, spl.second);
  return ans;
}

void display(node* a) {
  if (a == nullptr)
    return;
  display(a->l);
  cout << a->x << ' ';
  display(a->r);
}

signed main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  // freopen("input.txt", "r", stdin);
  string s;
  node* dd = nullptr;
  while (cin >> s) {
    if (s == "insert") {
      int x;
      cin >> x;
      dd = insert(dd, x);
    }
    if (s == "delete") {
      int x;
      cin >> x;
      dd = erase(dd, x);
    }
    if (s == "exists") {
      int x;
      cin >> x;
      if (find(dd, x) == nullptr)
        cout << "false\n";
      else
        cout << "true\n";
    }
    if (s == "next") {
      int x;
      cin >> x;
      auto ans = next(dd, x);
      cout << (ans == nullptr ? "none" : to_string(ans->x)) << '\n';
    }
    if (s == "prev") {
      int x;
      cin >> x;
      auto ans = prev(dd, x);
      cout << (ans == nullptr ? "none" : to_string(ans->x)) << '\n';
    }
  }
}