Maximum Consecutive Sum

You are given a list of n integers and an integer C. Your task is to find the maximum sum of any C consecutive elements from the list. If the list contains fewer than C elements, output -1.

The problem can be formally stated as follows:

Given an array A of size n and an integer C, if n < C then output -1. Otherwise, find the maximum value of the sum:

\( S = \sum_{i=j}^{j+C-1} A_i \)

where \( 0 \leq j \leq n-C \). Use the sliding window technique to solve this problem efficiently.

inputFormat

The input is given via standard input (stdin) as follows:

• The first line contains two space-separated integers: n (the number of elements in the list) and C (the number of consecutive elements to consider).
• The second line contains n space-separated integers representing the list.

outputFormat

Output a single integer, which is the maximum sum of C consecutive integers in the list. If the list has fewer than C elements, output -1.

10 4
1 2 3 4 5 6 7 8 9 10

34