#include <bits/stdc++.h>
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define rep(i,n) for (int i=0;i<(int)(n);i++)
#define codefor int test;scanf("%d",&test);while(test--)
#define INT(...) int __VA_ARGS__;in(__VA_ARGS__)
#define LL(...) ll __VA_ARGS__;in(__VA_ARGS__)
#define yes(ans) if(ans)printf("yes\n");else printf("no\n")
#define Yes(ans) if(ans)printf("Yes\n");else printf("No\n")
#define YES(ans) if(ans)printf("YES\n");else printf("NO\n")
#define vector1d(type,name,...) vector<type>name(__VA_ARGS__)
#define vector2d(type,name,h,...) vector<vector<type>>name(h,vector<type>(__VA_ARGS__))
#define vector3d(type,name,h,w,...) vector<vector<vector<type>>>name(h,vector<vector<type>>(w,vector<type>(__VA_ARGS__)))
#define umap unordered_map
#define uset unordered_set
using namespace std;
using ll = long long;
const int MOD=1000000007;
const int MOD2=998244353;
const int INF=1<<30;
const ll INF2=(ll)1<<60;
//入力系
void scan(int& a){scanf("%d",&a);}
void scan(long long& a){scanf("%lld",&a);}
template<class T,class L>void scan(pair<T, L>& p){scan(p.first);scan(p.second);}
template<class T> void scan(T& a){cin>>a;}
template<class T> void scan(vector<T>& vec){for(auto&& it:vec)scan(it);}
void in(){}
template <class Head, class... Tail> void in(Head& head, Tail&... tail){scan(head);in(tail...);}
//出力系
void print(const int& a){printf("%d",a);}
void print(const long long& a){printf("%lld",a);}
void print(const double& a){printf("%.15lf",a);}
template<class T,class L>void print(const pair<T, L>& p){print(p.first);putchar(' ');print(p.second);}
template<class T> void print(const T& a){cout<<a;}
template<class T> void print(const vector<T>& vec){if(vec.empty())return;print(vec[0]);for(auto it=vec.begin();++it!= vec.end();){putchar(' ');print(*it);}}
void out(){putchar('\n');}
template<class T> void out(const T& t){print(t);putchar('\n');}
template <class Head, class... Tail> void out(const Head& head,const Tail&... tail){print(head);putchar(' ');out(tail...);}
//デバッグ系
template<class T> void dprint(const T& a){cerr<<a;}
template<class T> void dprint(const vector<T>& vec){if(vec.empty())return;cerr<<vec[0];for(auto it=vec.begin();++it!= vec.end();){cerr<<" "<<*it;}}
void debug(){cerr<<endl;}
template<class T> void debug(const T& t){dprint(t);cerr<<endl;}
template <class Head, class... Tail> void debug(const Head& head, const Tail&... tail){dprint(head);cerr<<" ";debug(tail...);}
ll intpow(ll a, ll b){ ll ans = 1; while(b){ if(b & 1) ans *= a; a *= a; b /= 2; } return ans; }
ll modpow(ll a, ll b, ll p){ ll ans = 1; while(b){ if(b & 1) (ans *= a) %= p; (a *= a) %= p; b /= 2; } return ans; }
ll updivide(ll a,ll b){if(a%b==0) return a/b;else return (a/b)+1;}
template<class T> void chmax(T &a,const T b){if(b>a)a=b;}
template<class T> void chmin(T &a,const T b){if(b<a)a=b;}

struct graph{
    int _n;
    vector<vector<int>> g;
    graph() : _n(0) {}
    graph(int n) : _n(n), g(n) {}
    void merge(int a,int b){
        g[a].push_back(b);
        g[b].push_back(a);
    }
    struct node{
        int parent=-1;
        int depth=-1;
        int part_node=-1;
        vector<int> children;
    };
    vector<node> tree;
    void generate_tree(int root){
        queue<int> next;
        int x;
        tree.resize(_n);
        tree[root].parent=-1;
        tree[root].depth=0;
        next.push(root);
        while(!next.empty()){
            x=next.front();
            next.pop();
            for(int i=0;i<g[x].size();i++){
                if(tree[g[x][i]].depth==-1){
                    next.push(g[x][i]);
                    tree[x].children.push_back(g[x][i]);
                    tree[g[x][i]].parent=x;
                    tree[g[x][i]].depth=tree[x].depth+1;
                }
            }
        }
    }
    int make_partnode(int x){
        if(tree[x].part_node!=-1){
            return tree[x].part_node;
        }else if(tree[x].children.size()==0){
            return tree[x].part_node=1;
        }else{
            int d=1;
            for(int i=0;i<tree[x].children.size();i++){
                d+=make_partnode(tree[x].children[i]);
            }
            return tree[x].part_node=d;
        }
    }
};

int main(){
    INT(n);
    graph t(n);
    map<pair<int,int>,int> Map;
    int a,b,c;
    rep(i,n-1){
        in(a,b,c);
        Map[make_pair(min(a,b)-1,max(a,b)-1)]=c;
        t.merge(a-1,b-1);
    }
    t.generate_tree(0);
    t.make_partnode(0);
    int p;
    ll ans=0;
    for(int i=1;i<n;i++){
        p=t.tree[i].parent;
        ans+=(ll)Map[make_pair(min(i,p),max(i,p))]*t.tree[i].part_node*(n-t.tree[i].part_node);
    }
    out(ans*2);
}