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

ans = 0
SUM = 0
for i in range(N-M+1):
    if i == 0:
        for j in range(M):
            SUM += max(A[j]-B[j], 0)
    else:
        SUM -= max(A[i-1]-B[i-1], 0)
        SUM += max(A[i+M-1]-B[i+M-1], 0)
    ans = max(ans, SUM)

print(ans)