int tree_size;
    cin >> tree_size;

    vector <Node> tree(tree_size + 1);
    vector <bool> is_root(tree_size + 1, true);
    is_root[0] = false;

    for (int i = 1; i <= tree_size; ++i) {
        int left, right;
        cin >> left >> right;
        is_root[left] = false;
        is_root[right] = false;

        tree[i].val = i;
        if (left == 0) {
            tree[i].left = nullptr;
        } else {
            tree[i].left = &tree[left];
        }

        if (right == 0) {
            tree[i].right = nullptr;
        } else {
            tree[i].right = &tree[right];
        }
    }

    Node* root = nullptr;
    for (int i = 1; i < is_root.size(); ++i) {
        if (is_root[i]) {
            root = &tree[i];
            break;
        }
    }