N, K = [int(i) for i in input().split()]
X = [int(i) for i in input().split()]
A = [int(i) for i in input().split()]

ans = 1
cur = 1e50
for i in reversed(range(K - 1)):
    cur = min(cur, X[i + 1] - A[i + 1])
    if cur > X[i]:
        break
    ans += 1

cur = -1e50
for i in range(K, N):
    cur = max(cur, X[i - 1] + A[i - 1])
    if cur < X[i]:
        break
    ans += 1

print(ans)