N, K = map(int, input().split())
X = list(map(int, input().split()))
A = list(map(int, input().split()))
K -= 1
Q = [K]
lp = X[K]
rp = X[K]
li = K
ri = K
rlimit = K
ans = 0
while Q:
    x = Q.pop()
    if X[x] - A[x] < lp:
        lp = X[x] - A[x]
        while 0 < li and lp <= X[li - 1]:
            li -= 1
            Q.append(li)
    if rp < X[x] + A[x]:
        rp = X[x] + A[x]
        while ri < N - 1 and X[ri + 1] <= rp:
            ri += 1
            Q.append(ri)
print(ri - li + 1)