2,650. Not to Eat A; Not to Eat A+B

Hilchos Shevuos 4:14

Let’s say that someone took an oath not to eat figs, followed by oath not to eat a combination of figs and grapes. This person forgot, ate figs, and put aside an offering. He later forgot and ate grapes. In such a case, he isn’t liable for eating grapes because it’s like eating half the requisite volume for culpability, for which one doesn’t bring an offering.

Hilchos Shevuos 4:15

The same is true if one took an oath not to eat ten of something, followed by an oath not to eat ten plus nine. If he ate ten and put aside an offering, after which he forgot and ate nine, it’s like eating half the requisite volume for culpability, for which one doesn’t bring an offering, because his latter oath was not to eat 19 of the item.