n,k = input().split()
x = [-2**60] + list(map(int,input().split())) + [2**60]
a = [0] + list(map(int,input().split())) + [0]
l = r = int(k)
L,R = x[r]-a[r], x[r]+a[r]
while L <= x[l] or x[r] <= R:
    if L <= x[l]: L,R,l = min(L,x[l]-a[l]), max(R,x[l]+a[l]), l-1
    if x[r] <= R: L,R,r = min(L,x[r]-a[r]), max(R,x[r]+a[r]), r+1
print(r-l-1)