typedef struct s_node {
        int           value;
        struct s_node *right;
        struct s_node *left;
} Node;

Node* recurse(Node* root) {

    if (!root)
        return 0;

    if (root->left) {

        Node* left = recurse(root->left);
        while (left->right)
            left = left->right;
        left->right = root;
        root->left = left;

    }
    if (root->right) {

        Node* right = recurse(root->right);
        while (right->left)
            right = right->left;
        right->left = root;
        root->right = right;
    }
    return root;
}

Node* convert_bst(Node* bst) {
    if (!bst)
        return 0;
    recurse(bst);
    Node* left = bst;
    Node* right = bst;
    while (left->left)
        left = left->left;
    while (right->right)
        right = right->right;
    left->left = right;
    right->right = left;
    return left;
}