import sys
input = sys.stdin.readline
N, M = map(int, input().split())
A = list(map(int, input().split()))
B = list(map(int, input().split()))

souwa = [0] * (N + 1)
for i in range(N):
    souwa[i + 1] = souwa[i] + max(A[i] - B[i], 0)

print(max(souwa[i + M] - souwa[i] for i in range(N - M + 1)))