// yukicoder: 872 All Tree Path
// 2019.9.6 bal4u

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef long long ll;

//// 高速入力
#if 1
#define gc() getchar_unlocked()
#else
#define gc() getchar()
#endif

int in() {   // 非負整数の入力
	int n = 0, c = gc();
	do n = 10 * n + (c & 0xf); while ((c = gc()) >= '0');
	return n;
}

int N;
int hi[200005], *to[200005], *w[200005];
ll ans;

int dfs(int now, int par) {
	int i, j, s, f;
	
	s = 1;
	for (i = 0; i < hi[now]; i++) if ((j = to[now][i]) != par) {
		s += (f = dfs(j, now));
		ans += ((ll)w[now][i] * f * (N-f)) << 1;
	}
	return s;
}
				
int main()
{
	int i, k, u, v;
	int *memo, sz;
	
	N = in();
	memo = malloc(N*sizeof(int)*3);
	sz = 0; for (i = 1; i < N; i++) {
		u = in()-1, v = in()-1;
		memo[sz++] = u, memo[sz++] = v, memo[sz++] = in();
		hi[u]++, hi[v]++;
	}
	for (i = 0; i < N; i++) if (hi[i]) {
		to[i] = malloc(hi[i] * sizeof(int));
		w[i] = malloc(hi[i] * sizeof(int));
	}
	memset(hi, 0, sizeof(int)*N);
	
	i = 0; while (i < sz) {
		u = memo[i++], v = memo[i++];
		k = hi[u]++, to[u][k] = v, w[u][k] = memo[i];
		k = hi[v]++, to[v][k] = u, w[v][k] = memo[i++];
	}
	
	dfs(0, -1);
	printf("%lld\n", ans);
	return 0;
}