(n,),*e=[[*map(int,s.split())]for s in open(0)]
uv=e[:n-1]
xy=e[n-1:]
M=1<<64
def f(i,edges):
  ret=[-1]*n
  g=[[]for _ in range(n)]
  for u,v in edges:
    g[u-1]+=v-1,
    g[v-1]+=u-1,
  q=[i]
  ret[i]=0
  while q:
    p=q.pop()
    for v in g[p]:
      if ret[v]<0:
        q+=v,
        ret[v]=ret[p]+1
  return ret
ans=0
for p in range(n):
  da=f(p,uv)
  db=f(p,xy)
  for q in range(n):
    ans+=da[q]*db[q]
    ans%=M
print(ans)