Minimum sample size for a size constraint

Let $X_1,X_2,…,X_n$ be a random sample from a $N(\theta,1)$ distribution. To test $H_0:\theta=0$ against $H_1:\theta=1$, assume that the critical region is given by $\frac1n\sum_{i=1}^nX_i>\frac34$. Then the minimum sample size required so that $P(\text{Type I error})\le0.05$ is