def main():
    N, K = map(int, input().split())
    X = list(map(int, input().split()))
    A = list(map(int, input().split()))
    frog = 1
    if N >= 2:
        for i in range(K - 1, -1, -1):
            if X[i - 2] + A[i - 1] >= X[i - 1]:
                frog += 1
            else:
                break
        for i in range(K - 1, N - 1):
            if X[i - 1] + A[i - 1] >= X[i]:
                frog += 1
            else:
                break
    print(frog)

if __name__ == "__main__":
    main()