#include <bits/stdc++.h>
using namespace std;

int N;
vector<pair<int, int>> edges[200000];

int64_t ans = 0;
int dfs(int i, int p){
    int num = 1;
    for(auto& e : edges[i]){
        if(e.first == p) continue;
        int add = dfs(e.first, i);
        ans += 2LL * e.second * add * (N-add);
        num += add;
    }
    return num;
}

int main(){
    cin >> N;
    for(int i=0; i<N-1; i++){
        int a, b, c;
        cin >> a >> b >> c;
        edges[a-1].emplace_back(b-1, c);
        edges[b-1].emplace_back(a-1, c);
    }

    dfs(0, -1);
    cout << ans << endl;
    return 0;
}