7. Square $A B C D$ has a side length of $1, A B, A D$ each have a point $P, Q$, if the perimeter of $\triangle A P Q$ is 2, find the degree of $\angle P C Q$.

The square $A B C D$ has a side length of 1, and points $P$ and $Q$ are on $A B$ and $A D$ respectively. If the perimeter of $\triangle A P Q$ is 2, find the degree of $\angle P C Q$.