local n = io.read("*n")
local node = {}
for i = 1, n do
  node[i] = {}
  node[i].edge, node[i].dup, node[i].asked, node[i].edgenum = {}, 1, false, 0
end
for i = 1, n - 1 do
  local u, v, w = io.read("*n", "*n", "*n")
  node[u].edge[v] = w
  node[u].edgenum = node[u].edgenum + 1
  node[v].edge[u] = w
  node[v].edgenum = node[v].edgenum + 1
end
local tasks = {}
local tasknum = 0
local done = 0
for i = 1, n do
  if node[i].edgenum == 1 then
    table.insert(tasks, i)
    tasknum = tasknum + 1
  end
end
local ret = 0LL
while done < tasknum do
  done = done + 1
  local idx = tasks[done]
  node[idx].asked = true
  for dst, len in pairs(node[idx].edge) do
    if not node[dst].asked then
      local d = node[idx].dup
      ret = ret + 1LL * d * (n - d) * len
      node[dst].edgenum = node[dst].edgenum - 1
      node[dst].dup = node[dst].dup + node[idx].dup
      if node[dst].edgenum == 1 then
        table.insert(tasks, dst)
        tasknum = tasknum + 1
      end
      break
    end
  end
end
ret = ret * 2LL
local str = tostring(ret):gsub("LL", "")
print(str)