Max Subarray Sum with Constraints

You are given an integer array nums. Your goal is to find the maximum sum of a continuous subarray. However, the subarray must contain at least one element and its sum must not exceed a given limit x. Your task is to implement a function that takes these inputs and outputs the maximum sum or -1 if no such subarray exists. Input Format: - The first line contains an integer n (the length of the array). - The second line contains n space-separated integers (the elements of the array nums). - The third line contains an integer x (the upper limit of the subarray sum). Output Format: - Output a single integer representing the maximum sum of the valid subarray, or -1 if no valid subarray exists. Example: Input: 5 1 2 3 4 5 7 Output: 7