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