#define _USE_MATH_DEFINES
#include "bits/stdc++.h"
using namespace std;
#define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i))
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define MT make_tuple
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
#define RT return
using ll = long long;
using pii = pair<int, int>;
using vi = vector<int>;
using vll = vector<ll>;

vector<pii> G[200005];
ll ans;
int N;

int dfs(int u, int p) {
    int res = 1;
    each(e, G[u]) {
        if (e.first != p) {
            int num =  dfs(e.first, u);
            ans += (ll)num * (N - num) * e.second * 2;
            res += num;
        }
    }
    return res;
}

void solve() {
    cin >> N;
    rep(i, N - 1) {
        int u, v, w;
        cin >> u >> v >> w;
        --u; --v;
        G[u].emplace_back(v, w);
        G[v].emplace_back(u, w);
    }

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

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout << fixed << setprecision(15);
	solve();
	return 0;
}