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