CISCO

There is a tree $T$ with $N$ vertices, numbered $1$ through $N$. For each $1≤i≤N−1$, the $i-th$ edge connects vertices $ai$ and $bi$. Cisco is constructing a directed graph $T'$ by arbitrarily assigning direction to each edge in $T$. (There are $2N−1$ different ways to construct $T'$.) For a fixed $T'$, we will define $d(s, t)$ for each $1≤s$, $t≤N$, as follows: $d(s, t)$=(The number of edges t