How many times a week do you have to eat omega 3?

I don't want to eat fish because it is more expensive than other foods but I know its important to get omega 3 so I want to know how many times a week I should be consuming fish if it is my only source of omega 3. Is twice a week enough or should I eat sardines since its a cheap source of omega 3 and if I eat sardines, how often should I eat them?
How many times a week do you have to eat omega 3?
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