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]
l = k-1
lx = X[k]-A[k]

while True:
    upd = 0
    if r < n and X[r] <= rx:
        rx = max(rx,X[r]+A[r])
        lx = min(lx,X[r]-A[r])
        r += 1
        upd = 1

    if 0 <= l and X[l] >= lx:
        rx = max(rx,X[l]+A[l])
        lx = min(lx,X[l]-A[l])
        l -= 1
        upd = 1
    if upd == 0:
        break
print(r-l-1)