Actually, my dentist recommends flossing BEFORE brushing.
The reason being, when you brush then floss, if there's anything you get out from between your teeth, it's still there.
If you floss first, then whatever you get out from between your teeth is brushed away.
On occasions I will floss first if there is lot of food
stuck between teeth. The important thing is to floss.
The remaining food will breed bacteria which attack gums
and tooth itself.