How much weight would I have to gain to make my boos perportionate?

So I'm pretty slim and have really big boobs, but I want to make them more proportionate so I'm panning on gaining some weight. I'm a 32f and I would hope that if I gain weight I can get them to look like Cs or Bs. So do you know how much I've got to gain, to make things work?
How much weight would I have to gain to make my boos perportionate?
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