Faceslapping to warm the slave up

Description: I made the slave wait for me outside for a few hours in just a t-shirt - with almost freezing temperatures! obviously, he's very cold and shivering when i take him inside ... and i'll now help him get warm again! and nothing heats up a slave's skin like hard slaps to the face ... a lot of hard slaps! it doesn't take long until the skin's glowing red and the slave is trembling in pain ... so i decide to send him outside for another hour ... and afterwards we'll continue with the slaps ... and then he'll go into the cold again ... how many rounds should i make him endure?!