Edge = Struct.new(:from, :to, :weight)
N = gets.to_i
G = Array.new(N + 1){ [] } 
T = Array.new(N + 1){ [] } # tree as root was 1
C = Array.new(N + 1) # node count of subtree

(1 ... N).each do 
  u,v,w = gets.split.map(&:to_i)
  G[u] << Edge.new(u, v, w)
  G[v] << Edge.new(v, u, w)
end

used = Array.new(N + 1)
stack = [1]
used[1] = true
order = []

until stack.empty?
  u = stack.pop
  order << u
  
  G[u].each do |e|
    unless used[e.to]
      used[e.to] = true
      stack << e.to 
      T[u] << e
    end
  end
end

order.reverse_each{|u| C[u] = T[u].inject(1){|c, e| c + C[e.to] } }
ans = T.flatten.inject(0){|s, e| s +  e.weight * C[e.to] * (N - C[e.to]) * 2}

puts ans