In Matthew 17, what did Jesus say to his disciples when they couldn't cure a lunatic?

Oh faithless and perverse generation! How long must I be with you?

And when they were come to the multitude, there came to him a certain man, kneeling down to him, and saying,

Lord, have mercy on my son: for he is lunatick, and sore vexed: for ofttimes he falleth into the fire, and oft into the water.

And I brought him to thy disciples, and they could not cure him.

Then Jesus answered and said, O faithless and perverse generation, how long shall I be with you? how long shall I suffer you? Matthew 17:14-17