use std::io::*;

fn dfs(v: usize, p: usize, graph: &Vec<Vec<usize>>, size: &mut Vec<usize>) -> usize {
    let mut res = 1;
    for &nv in graph[v].iter() {
        if nv != p {
            res += dfs(nv, v, &graph, size);
        }
    }
    size[v] = res;
    res
}

fn main() {
    let mut s: String = String::new();
    std::io::stdin().read_to_string(&mut s).ok();
    let mut itr = s.trim().split_whitespace();
    let n: usize = itr.next().unwrap().parse().unwrap();

    let mut graph: Vec<Vec<usize>> = vec![Vec::new(); n];
    let mut edges: Vec<(usize, usize, usize)> = Vec::new();
    for _ in 0..n - 1 {
        let u: usize = itr.next().unwrap().parse::<usize>().unwrap() - 1;
        let v: usize = itr.next().unwrap().parse::<usize>().unwrap() - 1;
        let w: usize = itr.next().unwrap().parse().unwrap();
        graph[u].push(v);
        graph[v].push(u);
        edges.push((u, v, w));
    }

    let mut size: Vec<usize> = vec![0; n];
    dfs(0, 0, &graph, &mut size);
    let mut ans = 0;
    for &(u, v, w) in edges.iter() {
        let small = std::cmp::min(size[u], size[v]);
        ans += (n - small) * small * w * 2;
    }

    println!("{}", ans);
}