n,k = map(int,input().split())
INF = 10**18
x = [-INF] + list(map(int,input().split())) + [INF]
a = [0] + list(map(int,input().split())) + [0]
l = r = k
L,R = x[k]-a[k], x[k]+a[k]
while L <= x[l] or x[r] <= R:
    if L <= x[l]:
        L = min(L,x[l]-a[l])
        R = max(R,x[l]+a[l])
        l -= 1
    if x[r] <= R:
        L = min(L,x[r]-a[r])
        R = max(R,x[r]+a[r])
        r += 1
print(r-l-1)