n, k = map(int, input().split())
x = list(map(int, input().split()))
a = list(map(int, input().split()))
cur_back, cur_front = k-1, k-1
while cur_back > 0 and x[cur_back]-a[cur_back] <= x[cur_back-1]:
    cur_back -= 1
while cur_front < n-1 and x[cur_front]+a[cur_front] >= x[cur_front+1]:
    cur_front += 1
print(cur_front-cur_back+1)