#include<bits/stdc++.h>
using namespace std;
#define ALL(x) x.begin(),x.end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define debug(v) cout<<#v<<":";for(auto x:v){cout<<x<<' ';}cout<<endl;
#define INF 1000000000
#define mod 1000000007
using ll=long long;
const ll LINF=1001002003004005006ll;
int dx[]={1,0,-1,0};
int dy[]={0,1,0,-1};
ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
template<class T>bool chmax(T &a,const T &b){if(a<b){a=b;return true;}return false;}
template<class T>bool chmin(T &a,const T &b){if(b<a){a=b;return true;}return false;}

int n;
vector<vector<pair<int,ll>>> g;
ll ans;

ll dfs(int pre,int now){
    ll ret=1;
    for(auto p:g[now])if(p.first!=pre){
        ll a=dfs(now,p.first);
        ans+=p.second*a*(n-a);
        ret+=a;
    }
    return ret;
}


signed main(){
    cin.tie(0);
    ios::sync_with_stdio(0);

    cin>>n;
    g.resize(n);
    rep(i,n-1){
        int u,v,c;cin>>u>>v>>c;u--,v--;
        g[u].push_back(make_pair(v,c));
        g[v].push_back(make_pair(u,c));
    }
    dfs(-1,0);
    cout<<ans*2<<endl;
    return 0;
}