import java.io.*
import java.util.*
import kotlin.math.*
 
fun main(args: Array<String>) = with(BufferedReader(InputStreamReader(System.`in`))) {
 
	val (N, K) = readLine()!!.split(" ").map{it.toInt()}
    val numbers = readLine()!!.split(" ").map{it.toInt()}
	var sum = 0
	var answer = 0
 
	for(i in 0 until K) sum += numbers[i]
	for(i in K until N){
		answer = max(sum, answer)
		sum-=numbers[i-K]
		sum+=numbers[i]
	}
 
	BufferedWriter(OutputStreamWriter(System.`out`)).use{
		it.write("$answer")
		it.flush()
	}
}

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MTAgNQozIC0yIC00IC05IDAgMyA3IDEzIDggLTM=

10 5
3 -2 -4 -9 0 3 7 13 8 -3