import java.util.*;
import java.lang.*;
import java.io.*;

// The main method must be in a class named "Main".
class Main {
    
    public static int[] prefixSum(int [] arr){
        int n = arr.length;
        int psum[] = new int[n];
        psum[0] = arr[0];
        for(int i=1 ; i<n ; i++){
            psum[i] = psum[i-1] + arr[i]; 
        }
        return psum ;
    }

    
    public static int maxSumforlenk(int [] arr , int k ){
        
        int n = arr.length;
        int psum[] = prefixSum(arr);
        
        int maxSum = psum[k-1];

        for(int i=k ; i<n ; i++){
            int sum =psum[i] - psum[i-k];
            maxSum = Math.max(maxSum, sum);
        }

        return maxSum;
    }

    
    public static void main(String[] args) {
        int [] arr = {2,3,9,-1,7,1,0};
        int k = 4 ;
        System.out.println("MAXIMUM SUM WITH Length : 4 = " + maxSumforlenk(arr,k));
    }
}