#pragma GCC optimize ("Ofast")
#include<bits/stdc++.h>
using namespace std;
void *wmem;
template<class T> inline void walloc1d(T **arr, int x, void **mem = &wmem){
  static int skip[16]={0, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1};
  (*mem) = (void*)( ((char*)(*mem)) + skip[((unsigned long long)(*mem)) & 15] );
  (*arr)=(T*)(*mem);
  (*mem)=((*arr)+x);
}
inline void rd(int &x){
  int k, m=0;
  x=0;
  for(;;){
    k = getchar_unlocked();
    if(k=='-'){
      m=1;
      break;
    }
    if('0'<=k&&k<='9'){
      x=k-'0';
      break;
    }
  }
  for(;;){
    k = getchar_unlocked();
    if(k<'0'||k>'9'){
      break;
    }
    x=x*10+k-'0';
  }
  if(m){
    x=-x;
  }
}
inline void wt_L(char a){
  putchar_unlocked(a);
}
inline void wt_L(long long x){
  char f[20];
  int m=0, s=0;
  if(x<0){
    m=1;
    x=-x;
  }
  while(x){
    f[s++]=x%10;
    x/=10;
  }
  if(!s){
    f[s++]=0;
  }
  if(m){
    putchar_unlocked('-');
  }
  while(s--){
    putchar_unlocked(f[s]+'0');
  }
}
struct graph{
  int N, **edge, *es;
  void setEdge(int N__, int M, int A[], int B[], void **mem = &wmem){
    int i;
    N = N__;
    walloc1d(&es, N, mem);
    walloc1d(&edge, N, mem);
    for(i=0;i<(N);i++){
      es[i] = 0;
    }
    for(i=0;i<(M);i++){
      es[A[i]]++;
      es[B[i]]++;
    }
    for(i=0;i<(N);i++){
      walloc1d(&edge[i], es[i], mem);
    }
    for(i=0;i<(N);i++){
      es[i] = 0;
    }
    for(i=0;i<(M);i++){
      edge[A[i]][es[A[i]]++] = B[i];
      edge[B[i]][es[B[i]]++] = A[i];
    }
  }
}
;
template<class T> struct wgraph{
  T **cost;
  graph g;
  int N, **edge, *es;
  void setEdge(int N__, int M, int A[], int B[], T C[], void **mem = &wmem){
    int i;
    N = N__;
    walloc1d(&es, N, mem);
    for(i=0;i<(N);i++){
      es[i] = 0;
    }
    for(i=0;i<(M);i++){
      es[A[i]]++;
      es[B[i]]++;
    }
    walloc1d(&edge, N, mem);
    for(i=0;i<(N);i++){
      walloc1d(&edge[i], es[i], mem);
    }
    walloc1d(&cost, N, mem);
    for(i=0;i<(N);i++){
      walloc1d(&cost[i], es[i], mem);
    }
    for(i=0;i<(N);i++){
      es[i] = 0;
    }
    for(i=0;i<(M);i++){
      edge[A[i]][es[A[i]]] = B[i];
      edge[B[i]][es[B[i]]] = A[i];
      cost[A[i]][es[A[i]]++] = C[i];
      cost[B[i]][es[B[i]]++] = C[i];
    }
    g.N = N;
    g.es = es;
    g.edge = edge;
  }
}
;
char memarr[96000000];
int N;
int A[200000];
int B[200000];
int C[200000];
wgraph<int> g;
int cnt[200000];
long long res;
int dfs(int n, int b){
  int i, k, r=1, tmp;
  for(i=0;i<(g.es[n]);i++){
    k = g.edge[n][i];
    if(k==b){
      continue;
    }
    r += (tmp = dfs(k, n));
    res += (long long)2 * tmp * (N-tmp) * g.cost[n][i];
  }
  return r;
}
int main(){
  wmem = memarr;
  rd(N);
  {
    int Lj4PdHRW;
    for(Lj4PdHRW=0;Lj4PdHRW<(N-1);Lj4PdHRW++){
      rd(A[Lj4PdHRW]);A[Lj4PdHRW] += (-1);
      rd(B[Lj4PdHRW]);B[Lj4PdHRW] += (-1);
      rd(C[Lj4PdHRW]);
    }
  }
  g.setEdge(N,N-1,A,B,C);
  dfs(0, -1);
  wt_L(res);
  wt_L('\n');
  return 0;
}
// cLay varsion 20190830-1

// --- original code ---
// int N, A[2d5], B[2d5], C[2d5];
// wgraph<int> g;
// 
// int cnt[2d5];
// ll res;
// 
// int dfs(int n, int b){
//   int i, k;
//   int r = 1, tmp;
// 
//   rep(i,g.es[n]){
//     k = g.edge[n][i];
//     if(k==b) continue;
//     r += (tmp = dfs(k, n));
//     res += (ll)2 * tmp * (N-tmp) * g.cost[n][i];
//   }
// 
//   return r;
// }
// 
// {
//   rd(N,(A--,B--,C)(N-1));
//   g.setEdge(N,N-1,A,B,C);
//   dfs(0, -1);
//   wt(res);
// }