import sys
input = sys.stdin.readline

N, K = map(int, input().split())
K -= 1
X = list(map(int, input().split()))
A = list(map(int, input().split()))
l, r = K, K
ld, rd = X[K] - A[K], X[K] + A[K]
update = True

while update:
    update = False
    
    if l - 1 >= 0 and ld <= X[l-1]:
        update = True
        l -= 1
        ld = min(ld, X[l] - A[l])
        rd = max(rd, X[l] + A[l])
    
    if r + 1 < N and X[r+1] <= rd:
        update = True
        r += 1
        rd = max(rd, X[r] + A[r])
        ld = min(ld, X[r] - A[r])

print(r - l + 1)