//User function Template for Java

class Solution {

    public long maxSumWithK(long a[], long n, long k)

    {

        long sum = 0;

        long maxSum = 0;

        long prevElemSum = 0;

        for (int i = 0; i < k; i++) {

            sum = sum + a[i];

        }

        maxSum = sum;

        int m = 0;

        for(int i = (int)k; i < n; i++){

            sum = sum + a[i];

            maxSum = Math.max(sum, maxSum);

            prevElemSum = prevElemSum + a[m++];

            if(prevElemSum < 0){

                sum = sum - prevElemSum;

                prevElemSum = 0;

                maxSum = Math.max(sum, maxSum);

            }

        }

        return maxSum;

    }

}