n, k = map(int, input().split())
x = list(map(int, input().split()))
a = list(map(int, input().split()))
ans = 1
t = x[k - 1] - a[k - 1]
for i in range(k - 2, -1, -1):
    if t > x[i]:
        break
    t = min(t, x[i] - a[i])
    ans += 1
t = x[k - 1] + a[k - 1]
for i in range(k, n):
    if t < x[i]:
        break
    t = max(t, x[i] + a[i])
    ans += 1
print(ans)