n, k = map(int, input().split())
x = [0] + [int(i) for i in input().split()]
a = [0] + [int(i) for i in input().split()]

l = r = k
ld, rd = x[k]-a[k], x[k]+a[k]

update = True
while update:
    update = False
    while l-1 >= 1 and ld <= x[l-1]:
        update = True
        l -= 1
        ld = min(ld, x[l]-a[l])
        rd = max(rd, x[l]+a[l])
    while r+1 <= n and x[r+1] <= rd:
        update = True
        r += 1
        rd = max(rd, x[r]+a[r])
        ld = min(ld, x[r]-a[r])

print(r-l+1)