//#define NDEBUG
#include <cstddef>
#include <cstdint>
#include <iostream>
#include <vector>

namespace n91 {

using i8 = std::int_fast8_t;
using i32 = std::int_fast32_t;
using i64 = std::int_fast64_t;
using u8 = std::uint_fast8_t;
using u32 = std::uint_fast32_t;
using u64 = std::uint_fast64_t;
using isize = std::ptrdiff_t;
using usize = std::size_t;

constexpr usize operator"" _z(unsigned long long x) noexcept {
  return static_cast<usize>(x);
}

class rep {
  const usize f, l;

public:
  class itr {
    friend rep;
    usize i;
    constexpr itr(const usize x) noexcept : i(x) {}

  public:
    void operator++() noexcept { ++i; }
    constexpr usize operator*() const noexcept { return i; }
    constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
  };
  constexpr rep(const usize first, const usize last) noexcept
      : f(first), l(last) {}
  constexpr itr begin() const noexcept { return itr(f); }
  constexpr itr end() const noexcept { return itr(l); }
};
class revrep {
  const usize f, l;

public:
  class itr {
    friend revrep;
    usize i;
    constexpr itr(usize x) noexcept : i(x) {}

  public:
    void operator++() noexcept { --i; }
    constexpr usize operator*() const noexcept { return i; }
    constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
  };
  constexpr revrep(usize first, usize last) noexcept : f(--first), l(--last) {}
  constexpr itr begin() const noexcept { return itr(l); }
  constexpr itr end() const noexcept { return itr(f); }
};
template <class T> using vec_alias = std::vector<T>;
template <class T> auto md_vec(const usize n, const T &value) {
  return std::vector<T>(n, value);
}
template <class... Args> auto md_vec(const usize n, Args... args) {
  return std::vector<decltype(md_vec(args...))>(n, md_vec(args...));
}
template <class T> constexpr T difference(const T &a, const T &b) {
  return a < b ? b - a : a - b;
}
template <class T> T scan() {
  T ret;
  std::cin >> ret;
  return ret;
}

} // namespace n91

#include <algorithm>
#include <iostream>
#include <string>
#include <utility>

namespace n91 {

void main_() {
  const usize n = scan<usize>();
  struct edge_type {
    usize to;
    u64 cost;
  };
  auto g = md_vec(n, 0_z, edge_type());
  for (const auto i : rep(0_z, n - 1_z)) {
    const usize u = scan<usize>() - 1_z;
    const usize v = scan<usize>() - 1_z;
    const u64 w = scan<u64>();
    g[u].push_back({v, w});
    g[v].push_back({u, w});
  }

  u64 ans = static_cast<u64>(0);

  const auto dfs = [&](const auto &dfs, const usize v, const usize p) -> u64 {
    u64 ret = static_cast<u64>(1);
    for (const auto &e : g[v]) {
      if (e.to != p) {
        const u64 t = dfs(dfs, e.to, v);
        ans += (static_cast<u64>(n) - t) * t * e.cost;
        ret += t;
      }
    }
    return ret;
  };
  dfs(dfs, 0_z, n);

  std::cout << ans * static_cast<u64>(2) << std::endl;
}

} // namespace n91

int main() {
  n91::main_();
  return 0;
}