n,k=map(int,input().split())
A=list(map(int,input().split()))
C=list(map(int,input().split()))
X=[0]*51
def m(A,B):
    for i in range(1,len(A)):
        if A[i]:
            for j in range(max(1,i-k),min(len(A)-1,i+k)+1):
                if B[j]:
                    return True
    return False
for i in range(n):
    Y=X[:]
    Y[C[i]]=1
    Y[0]=A[i]
    C[i]=Y
for i in range(n+2):
    for j in range(n):
        C[j]
        C[(j+1)%n]
        if m(C[j],C[(j+1)%n]):
            C[(j+1)%n][0]+=C[j][0]
            C[j][0]=0
            for ii in range(1,51):
                if C[j][ii] or C[(j+1)%n][ii]:
                    C[j][ii]=1
                    C[(j+1)%n][ii]=1
                    
ans=0                    
for i in range(n):
    ans=max(ans,C[i][0])
print(ans)
#print(C)