def main():
    N, K = map(int, input().split())
    X = list(map(int, input().split()))
    A = list(map(int, input().split()))
    l = r = K - 1
    ld = X[K-1] - A[K-1]
    rd = X[K-1] + A[K-1]

    updated = True
    while updated:
        updated = False

        while l - 1 >= 0 and ld <= X[l - 1]:
            updated = True
            l -= 1
            ld = min(ld, X[l] - A[l])
            rd = max(rd, X[l] + A[l])
        
        while r + 1 < N and rd >= X[r + 1]:
            updated = True
            r += 1
            ld = min(ld, X[r] - A[r])
            rd = max(rd, X[r] + A[r])

    print(r - l + 1)



if __name__ == "__main__":
    main()