n, h = map(int, input().split())
a = list(map(int, input().split()))
b = list(map(int, input().split()))

maxv, sat, tired, curr_tired, r = 0, 0, 0, 0, 0

for l in range(n):
    
    while r < n and tired + curr_tired + b[r] <= h:
        curr_tired += b[r]  
        tired += curr_tired
        sat += a[r]  
        r += 1

    maxv = max(maxv, sat)

    if r > l:
        tired -= curr_tired
        curr_tired -= b[l] 
        sat -= a[l]
        
print(maxv)