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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