use std::vec::Vec;


fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>().split_whitespace().map(|e| e.parse().ok().unwrap()).collect()
}


fn main() {
  let n: usize = read();
  let mut g: Vec<Vec<(usize, usize)>> = vec![Vec::new(); n];
  for _ in 0..n-1 {
    let t: Vec<usize> = read_vec();
    g[t[0] - 1].push((t[1] - 1, t[2]));
    g[t[1] - 1].push((t[0] - 1, t[2]));
  }
  let mut visit = vec![false; n];
  let mut ans = 0;
  let dist = dfs(&g, &mut visit, 0,&mut ans);
  println!("{}", 2 * ans);
}

fn dfs(g: &Vec<Vec<(usize, usize)>>, visit: &mut Vec<bool>, now: usize, ans: &mut usize) -> usize {
  visit[now] = true;
  let n: usize = g.len();
  let mut res = 0;
  for &(node, cost) in &g[now] {
    if visit[node] { continue; }
    // 子ノードの個数
    let count = dfs(g, visit, node, ans);
    *ans += cost * count * (n - count);
    res += count;
  }

  res + 1
}