import bisect
n, k = map(int, input().split())
x = list(map(int, input().split()))
a = list(map(int, input().split()))

idxl = k-1
idxr = k-1
l = x[k-1]
r = x[k-1]
allfrog = 0

while True:
    if idxl >= 0 and l  <= x[idxl]:
        l = min(l, x[idxl] - a[idxl])
        r = max(r, x[idxl] + a[idxl])
        idxl -= 1
    if idxr < n and r  >= x[idxr]:
        l = min(l, x[idxr] - a[idxr])
        r = max(r, x[idxr] + a[idxr])
        idxr += 1
    if allfrog == idxr-idxl-1:
        print(idxr-idxl-1)
        break
    else:
        allfrog = idxr-idxl-1