An organometallic lithium compound, $\text{RLi}$, contains the nucleophile $\text{R}^-$. $\text{CH}_3\text{CH}_2\text{Li}$ undergoes reaction with pentan-2-one. This reaction proceeds by nucleophilic addition. During the first step, an anion is generated, and this is then protonated to give the final product. What organic product is produced?