n, m = map(int, input().split())
a = list(map(int, input().split()))
b = list(map(int, input().split()))

c = [0] * n
for i in range(n):
    c[i] = max(0, a[i] - b[i])

ans = 0
for i in range(n - m + 1):
    x = sum(c[i:i+m])
    ans = max(ans, x)

print(ans)