How much does a flat stomach matter to guys?

I'm a 15 yr old girl. I think I've got a pretty nice figure overall nice legs and hips and what not, I'm not super skinny but I'm not chubby either. However, my stomach is kind of far from flat. I try to work out to get in better shape but I just haven't noticed a difference yet.

I was wondering, how much does a flat stomach really matter to a guy?
How much does a flat stomach matter to guys?
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