Power of an MP Bernoulli test

Let $X_1,X_2,X_3$ be i.i.d. $\mathrm{Bin}(1,\theta)$ random variables. Consider the problem of testing the null hypothesis $H_0:\theta=\frac12$ against the alternative hypothesis $H_1:\theta=\frac14$ based on $X_1,X_2,X_3$. Then the power of the most powerful test of size $0.125$ is