# 想定誤答: i = N - M + 1 を見ていない（添え字ミス）
from itertools import accumulate

N, M = [int(s) for s in input().split()]
A = [int(s) for s in input().split()]
B = [int(s) for s in input().split()]

diff = [max(a - b, 0) for a, b in zip(A, B)]
acc = [0, *accumulate(diff)]

ans = 0
for i in range(N - M):
    ans = max(ans, acc[i + M] - acc[i])

print(ans)