You are given 2 arrays. Choose a subarray from the first array (arr1) and replace it with the corresponding subarray from the second array (arr2). After replacing the subarray, calculate the maximum consecutive subarray sum of the modified first array. Find the maximum subarray sum you can get by doing this operation. You can do this operation only once.

N is 10^5 and ai [-1e9, 1e9]

Im not able to think of better than n^2. Pls help