Common Ancestors

Ayush has two rooted trees. Each of them contains $N$ vertices (numbered $1$ through $N$); let's denote a vertex $v$ in tree $1$ by $v_1$ and a corresponding vertex $v$ in tree $2$ by $v_2$. For each tree $t$, any vertex on the path from the root to a vertex $v_t$ (including $v_t$) is an ancestor of $v_t$ and the depth of $v_t$ is the distance of $v_t$ from the root of tree $t$. For any integer