import sys
import math

# 入力高速化
#input = sys.stdin.readline
# 再帰回数上限
sys.setrecursionlimit(10**9)

# よくあるmod
#MOD = 1000000007
MOD = 998244353

def is_inside(y, x, h, w):
  return (0 <= y < h and 0 <= x < w)

def solve():
    N, M = map(int, input().split())
    A = list(map(int, input().split()))
    B = list(map(int, input().split()))
    ans = 0
    
    for j in range(M):
        if A[j] - B[j] > 0: ans += A[j] - B[j]
    cur = ans
    for i in range(1, N):
        if i + M - 1 > N-1: continue
        if i - 1 >= 0 and A[i - 1] - B[i - 1] > 0: cur -= A[i - 1] - B[i - 1]
        if A[i + M - 1] - B[i + M - 1] > 0: cur += A[i + M - 1] - B[i + M - 1]
        ans = max(ans, cur)
    print(ans)
    
if __name__ == '__main__':
    T = 1
    for _ in range(T):
        solve()