#include<bits/stdc++.h>
#define REP(i,n) for(int i=0,i##_len=(n);i<i##_len;++i)
#define rep(i,a,b) for(int i=int(a);i<int(b);++i)
#define All(x) (x).begin(),(x).end()
using namespace std;

int main(){
    int N;cin>>N;
    typedef pair<int,int> P;
    vector<vector<P>> graph(N);
    REP(i,N-1){
        int a,b,c; cin>>a>>b>>c;
        a--;b--;
        graph[a].push_back(P(c,b));
        graph[b].push_back(P(c,a));
    }
    long long ans=0;
    vector<int> leaf(N,0);
    vector<int> es(N,0);
    auto dfs=[&](auto &&f,int i,int pre)->int{
        for(auto e:graph[i]){
            if(e.second==pre){
                es[i]=e.first;
                continue;
            }
            leaf[i]+=f(f,e.second,i)+1;
        }
        for(auto e:graph[i]){
            if(e.second==pre) continue;
            ans+=(leaf[e.second]+1)*(N-leaf[e.second]-1)*e.first;
        }
        return leaf[i];
    };
    dfs(dfs,0,-1);
    
    cout<<2*ans<<endl;
}