def missing_num(arr):
    return 66 - sum(arr)

print(missing_num([3, 4, 7, 6, 9, 10, 1, 2, 5, 8]))

def missing_num(arr):
    return 66 - sum(arr)

print(missing_num([3, 4, 7, 6, 9, 10, 1, 2, 5, 8]))
