Aerobic exercise lasts for 40 minutes, and the weight loss effect is the best, but without this condition, you can practice for half an hour without exercising for 40 minutes. Although the effect can be a little worse, the effect is still obvious if you stick to it.

I suggest you do this. Take exercise first and ask your friends to bring you meals. Or prepare your own whole wheat bread and cereal, and prepare some eggs for lunch. The calories are definitely lower than those in your canteen.