N, K = map(int, input().split())
X = list(map(int, input().split()))
A = list(map(int, input().split()))
K -= 1
ans = 1

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

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

print(ans)