Best stretch of k days

Problem

Given the sales of each day, find the biggest total over any k days in a row. Print that total.

Example

Input

6 3
2 1 5 1 3 2

Output

The stretch 5 + 1 + 3 = 9 is the best.

Try the problem first. Open one hint at a time.

Hint 1

Add the first k values once. Then move the window one day at a time: add the new day and subtract the one that left.

Hint 2

Keep the biggest total you have seen so far.

Write your Python code, run it on the examples and submit it to hidden tests.