#include <iostream>

struct ListNode {
    int val;
    ListNode* next;
};

ListNode* middleNode(ListNode* head) {
    ListNode *slow = head, *fast = head;
    while (fast && fast->next) {
        slow = slow->next;
        fast = fast->next->next;
    }
    return slow;
}

ListNode* arr_to_list(const std::vector<int>& arr) {
    ListNode* head = nullptr;
    for (auto it = arr.rbegin(); it != arr.rend(); ++it) {
        head = new ListNode{*it, head};
    }
    return head;
}

int main() {
    auto node = arr_to_list({1, 2, 3, 4, 5, 6, 7, 8, 9, 10});
    std::cout << "Middle node is " << middleNode(node)->val << std::endl;
    return 0;
}