n,k = map(int,input().split())
X = list(map(int,input().split()))
A = list(map(int,input().split()))

k -= 1
r = k+1
rx = X[k]+A[k]
while r < n:
    if X[r] <= rx:
        rx = max(rx,X[r]+A[r])
        r += 1
    else:
        break

l = k-1
lx = X[k]-A[k]
while 0 <= l:
    if X[l] >= lx:
        lx = min(lx,X[l]-A[l])
        l -= 1
    else:
        break

print(r-l-1)