Maximum Sum

You are given a sequence of $n$ integers $a_1, a_2, \ldots, a_n$ and a positive integer $k$ ($1 \le k \le n$). Write a program that outputs the maximum value of the sum of $k$ consecutive terms

$$S_i = a_i + a_{i+1} + \cdots + a_{i+k-1} \quad (1 \le i \le n-k+1).$$

The first line contains a positive integer $n$ ($1 \le n \le 100000$) and a positive integer $k$ ($1 \le k \le n$) in this order, separated by a space. Each of the following lines holds one term of the sequence: line $1 + i$ (for $1 \le i \le n$) contains $a_i$ ($-10000 \le a_i \le 10000$).

Print a single line containing only the maximum value of $S_i$.