if !ENV['RUBY_THREAD_VM_STACK_SIZE']
  exec({'RUBY_THREAD_VM_STACK_SIZE'=>'1000000000'}, '/usr/bin/ruby', $0)
else
  N = gets.to_i
  E = Array.new(N + 1) { [] }
  V = Array.new(N + 1) { [] }

  (N - 1).times do
    u, v, w = gets.split.map(&:to_i)

    E[u] << [v, w]
    E[v] << [u, w]
  end

  def dfs1(u, cnt = 0, parent = -1)
    cnt = 0

    E[u].each do |v, w|
      next if v == parent

      v_cnt = dfs1(v, cnt, u)
      cnt += v_cnt
      V[u] << v_cnt
    end

    cnt + 1
  end

  $ans = 0

  def dfs2(u, v_cnt = 0, parent = -1)
    t_cnt = V[u].sum + v_cnt
    i = 0

    E[u].each do |v, w|
      next if v == parent

      cnt = V[u][i]
      $ans += 2 * w * (N - cnt) * cnt
      dfs2(v, t_cnt - cnt + 1, u)
      i += 1
    end
  end

  dfs1(1)
  dfs2(1)

  puts $ans
end