N, M = map(int, input().split())
A = list(map(int, input().split()))
B = list(map(int, input().split()))

S = 0
for i in range(M):
    S += max(0,A[i]-B[i])

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

print(ans)