Power of a Poisson sum test

Let $X_1,X_2,X_3$ be a random sample from a Poisson distribution with mean $\lambda$, $\lambda>0$. For testing $H_0:\lambda=\frac18$ against $H_1:\lambda=1$, a test rejects $H_0$ if and only if $X_1+X_2+X_3>1$. The power of this test is equal to __________ (round off to 2 decimal places)