I hate to disappoint you, but there is no such thing as a particular work-out that will make your stomach flat. If you want a flat stomach, you have to lose the “chub”. You do this through eating right and doing aerobic exercise. How long that will take will depend on how much you alter your diet, how much exercise you do, and how much weight you have to lose. I will say that it’s generally not recommended to lose more than a pound or two a week.