diff --git a/C4.cpp b/C4.cpp
new file mode 100644
index 0000000..95eb35b
--- /dev/null
+++ b/C4.cpp
@@ -0,0 +1,190 @@
+#include <iostream>
+#include <string>
+
+using std::cout;
+using std::cin;
+
+class AVL_tree {
+ public:
+  explicit AVL_tree(int k) : size(1), height(1), key(k), left(nullptr), right(nullptr) {}
+  AVL_tree *insert(AVL_tree *p, int k);
+  AVL_tree *remove(AVL_tree *p, int k);
+  int get_k_static(AVL_tree* p, int k);
+ private:
+  static int true_height(AVL_tree *p);
+  static int bifactor(AVL_tree *p);
+  void fixheight(AVL_tree *p);
+  AVL_tree *rotateright(AVL_tree *p);
+  AVL_tree *rotateleft(AVL_tree *q);
+  AVL_tree *balance(AVL_tree *p);
+  AVL_tree *findmin(AVL_tree *p);
+  AVL_tree *removemin(AVL_tree *p);
+  static int true_size(AVL_tree *p);
+  void fixsize(AVL_tree *p);
+  int size;
+  int height;
+  int key;
+  AVL_tree *left;
+  AVL_tree *right;
+  ~AVL_tree();
+};
+
+int AVL_tree::get_k_static(AVL_tree *p, int k) {
+  if (k == true_size(p->right) + 1){
+    return p->key;
+  }
+  if ( k > true_size(p->right) + 1 ){
+    return get_k_static(p->left, k - true_size(p->right) - 1);
+  }
+  if (k < true_size(p->right) + 1){
+    return get_k_static(p->right, k);
+  }
+  //return 0;
+}
+
+int AVL_tree::true_height(AVL_tree *p) {
+  if (p != nullptr) {
+    return p->height;
+  }
+  return 0;
+}
+
+int AVL_tree::true_size(AVL_tree *p){
+  if (p != nullptr) {
+    return p->size;
+  }
+  return 0;
+}
+
+int AVL_tree::bifactor(AVL_tree *p) {
+  return AVL_tree::true_height(p->right) - AVL_tree::true_height(p->left);
+}
+
+void AVL_tree::fixheight(AVL_tree *p) {
+  int hl = true_height(p->left);
+  int hr = true_height(p->right);
+  p->height = std::max(hl, hr) + 1;
+}
+
+void AVL_tree::fixsize(AVL_tree *p){
+  int hl = true_size(p->left);
+  int hr = true_size(p->right);
+  p->size = hl + hr + 1;
+}
+
+AVL_tree *AVL_tree::rotateright(AVL_tree *p) {
+  AVL_tree *q = p->left;
+  p->left = q->right;
+  q->right = p;
+  fixheight(p);
+  fixsize(p);
+  fixheight(q);
+
+  fixsize(q);
+  return q;
+}
+
+AVL_tree *AVL_tree::rotateleft(AVL_tree *q) {
+  AVL_tree *p = q->right;
+  q->right = p->left;
+  p->left = q;
+  fixheight(q);
+  fixsize(q);
+  fixheight(p);
+
+  fixsize(p);
+  return p;
+}
+
+AVL_tree *AVL_tree::balance(AVL_tree *p) {
+  fixheight(p);
+  fixsize(p);
+  if (bifactor(p) == 2) {
+    if (bifactor(p->right) < 0) {
+      p->right = rotateright(p->right);
+    }
+    return rotateleft(p);
+  }
+  if (bifactor(p) == -2) {
+    if (bifactor(p->left) > 0) {
+      p->left = rotateleft(p->left);
+    }
+    return rotateright(p);
+  }
+  return p;
+}
+
+AVL_tree *AVL_tree::insert(AVL_tree *p, int k) {
+  if (p == nullptr) return new AVL_tree(k);
+  if (k < p->key)
+    p->left = insert(p->left, k);
+  else
+    p->right = insert(p->right, k);
+  return balance(p);
+}
+
+AVL_tree *AVL_tree::findmin(AVL_tree *p) {
+  if (p->left != nullptr) {
+    return findmin(p->left);
+  } else return p;
+}
+
+
+AVL_tree *AVL_tree::removemin(AVL_tree *p) {
+  if (p->left == nullptr) {
+    return p->right;
+  }
+  p->left = removemin(p->left);
+  return balance(p);
+}
+
+AVL_tree *AVL_tree::remove(AVL_tree *p, int k) {
+  if (p == nullptr) {
+    return nullptr;
+  }
+  if (k < p->key) {
+    p->left = remove(p->left, k);
+  } else {
+    if (k > p->key) {
+      p->right = remove(p->right, k);
+    } else {
+      AVL_tree *q = p->left;
+      AVL_tree *r = p->right;
+      delete p;
+      if (r == nullptr) return q;
+      AVL_tree *min = findmin(r);
+      min->right = removemin(r);
+      min->left = q;
+      return balance(min);
+    }
+  }
+  return balance(p);
+}
+AVL_tree::~AVL_tree() {
+  left = nullptr;
+  right = nullptr;
+  height = 0;
+  key = 0;
+  size = 0;
+}
+
+int main() {
+  AVL_tree *L = nullptr;
+  int n;
+  cin >> n;
+  for (int i = 0; i < n; i++){
+    std::string c;
+    cin >> c;
+    int k;
+    cin >> k;
+    if (c == "+1" or c == "1"){
+      L = L->insert(L, k);
+    }
+    if (c == "-1"){
+      L = L->remove(L, k);
+    }
+    if (c == "0"){
+      cout<<L->get_k_static(L, k)<<"\n";
+    }
+  }
+}
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