#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")

#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <chrono>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }
#define COLOR(s) ("\x1b[" s "m")


struct Hld {
  int n, rt;
  // needs to be tree
  // vertex lists
  // modified in build(rt) (parent removed, heavy child first)
  vector<vector<int>> graph;
  vector<int> sz, par, dep;
  int zeit;
  vector<int> dis, fin, sid;
  // head vertex (minimum depth) in heavy path
  vector<int> head;

  Hld() : n(0), rt(-1), zeit(0) {}
  explicit Hld(int n_) : n(n_), rt(-1), graph(n), zeit(0) {}
  void ae(int u, int v) {
    assert(0 <= u); assert(u < n);
    assert(0 <= v); assert(v < n);
    graph[u].push_back(v);
    graph[v].push_back(u);
  }

  void dfsSz(int u) {
    sz[u] = 1;
    for (const int v : graph[u]) {
      auto it = std::find(graph[v].begin(), graph[v].end(), u);
      if (it != graph[v].end()) graph[v].erase(it);
      par[v] = u;
      dep[v] = dep[u] + 1;
      dfsSz(v);
      sz[u] += sz[v];
    }
  }
  void dfsHld(int u) {
    dis[u] = zeit++;
    const int deg = graph[u].size();
    if (deg > 0) {
      int vm = graph[u][0];
      int jm = 0;
      for (int j = 1; j < deg; ++j) {
        const int v = graph[u][j];
        if (sz[vm] < sz[v]) {
          vm = v;
          jm = j;
        }
      }
      swap(graph[u][0], graph[u][jm]);
      head[vm] = head[u];
      dfsHld(vm);
      for (int j = 1; j < deg; ++j) {
        const int v = graph[u][j];
        head[v] = v;
        dfsHld(v);
      }
    }
    fin[u] = zeit;
  }
  void build(int rt_) {
    assert(0 <= rt_); assert(rt_ < n);
    rt = rt_;
    sz.assign(n, 0);
    par.assign(n, -1);
    dep.assign(n, -1);
    dep[rt] = 0;
    dfsSz(rt);
    zeit = 0;
    dis.assign(n, -1);
    fin.assign(n, -1);
    head.assign(n, -1);
    head[rt] = rt;
    dfsHld(rt);
    assert(zeit == n);
    sid.assign(n, -1);
    for (int u = 0; u < n; ++u) sid[dis[u]] = u;
  }

  friend ostream &operator<<(ostream &os, const Hld &hld) {
    const int maxDep = *max_element(hld.dep.begin(), hld.dep.end());
    vector<string> ss(2 * maxDep + 1);
    int pos = 0, maxPos = 0;
    for (int j = 0; j < hld.n; ++j) {
      const int u = hld.sid[j];
      const int d = hld.dep[u];
      if (hld.head[u] == u) {
        if (j != 0) {
          pos = maxPos + 1;
          ss[2 * d - 1].resize(pos, '-');
          ss[2 * d - 1] += '+';
        }
      } else {
        ss[2 * d - 1].resize(pos, ' ');
        ss[2 * d - 1] += '|';
      }
      ss[2 * d].resize(pos, ' ');
      ss[2 * d] += std::to_string(u);
      if (maxPos < static_cast<int>(ss[2 * d].size())) {
        maxPos = ss[2 * d].size();
      }
    }
    for (int d = 0; d <= 2 * maxDep; ++d) os << ss[d] << '\n';
    return os;
  }

  bool contains(int u, int v) const {
    return (dis[u] <= dis[v] && dis[v] < fin[u]);
  }
  int lca(int u, int v) const {
    assert(0 <= u); assert(u < n);
    assert(0 <= v); assert(v < n);
    for (; head[u] != head[v]; ) (dis[u] > dis[v]) ? (u = par[head[u]]) : (v = par[head[v]]);
    return (dis[u] > dis[v]) ? v : u;
  }
  int jumpUp(int u, int d) const {
    assert(0 <= u); assert(u < n);
    assert(d >= 0);
    if (dep[u] < d) return -1;
    const int tar = dep[u] - d;
    for (u = head[u]; ; u = head[par[u]]) {
      if (dep[u] <= tar) return sid[dis[u] + (tar - dep[u])];
    }
  }
  int jump(int u, int v, int d) const {
    assert(0 <= u); assert(u < n);
    assert(0 <= v); assert(v < n);
    assert(d >= 0);
    const int l = lca(u, v);
    const int du = dep[u] - dep[l], dv = dep[v] - dep[l];
    if (d <= du) {
      return jumpUp(u, d);
    } else if (d <= du + dv) {
      return jumpUp(v, du + dv - d);
    } else {
      return -1;
    }
  }
  // [u, v) or [u, v]
  template <class F> void doPathUp(int u, int v, bool inclusive, F f) const {
    assert(contains(v, u));
    for (; head[u] != head[v]; u = par[head[u]]) f(dis[head[u]], dis[u] + 1);
    if (inclusive) {
      f(dis[v], dis[u] + 1);
    } else {
      if (v != u) f(dis[v] + 1, dis[u] + 1);
    }
  }
  // not path order, include lca(u, v) or not
  template <class F> void doPath(int u, int v, bool inclusive, F f) const {
    const int l = lca(u, v);
    doPathUp(u, l, false, f);
    doPathUp(v, l, inclusive, f);
  }

  // (vs, ps): compressed tree
  // vs: DFS order (sorted by dis)
  // vs[ps[x]]: the parent of vs[x]
  // ids[vs[x]] = x, not set for non-tree vertex
  vector<int> ids;
  pair<vector<int>, vector<int>> compress(vector<int> us) {
    // O(n) first time
    ids.resize(n, -1);
    std::sort(us.begin(), us.end(), [&](int u, int v) -> bool {
      return (dis[u] < dis[v]);
    });
    us.erase(std::unique(us.begin(), us.end()), us.end());
    int usLen = us.size();
    assert(usLen >= 1);
    for (int x = 1; x < usLen; ++x) us.push_back(lca(us[x - 1], us[x]));
    std::sort(us.begin(), us.end(), [&](int u, int v) -> bool {
      return (dis[u] < dis[v]);
    });
    us.erase(std::unique(us.begin(), us.end()), us.end());
    usLen = us.size();
    for (int x = 0; x < usLen; ++x) ids[us[x]] = x;
    vector<int> ps(usLen, -1);
    for (int x = 1; x < usLen; ++x) ps[x] = ids[lca(us[x - 1], us[x])];
    return make_pair(us, ps);
  }
};

////////////////////////////////////////////////////////////////////////////////


// build: O(n log(n)) time/space
// operator(): O(1) time
struct Lca {
  int n, rt;
  vector<vector<int>> graph;
  vector<int> par, dep, su;
  int usLen;
  vector<int> us;
  vector<int> buffer;
  vector<int *> mn;

  Lca() : n(0), rt(-1), usLen(0) {}
  explicit Lca(int n_) : n(n_), rt(-1), graph(n), usLen(0) {}
  void ae(int u, int v) {
    assert(0 <= u); assert(u < n);
    assert(0 <= v); assert(v < n);
    graph[u].push_back(v);
    graph[v].push_back(u);
  }

  void dfs(int u, int p) {
    us[su[u] = usLen++] = u;
    for (const int v : graph[u]) if (p != v) {
      par[v] = u;
      dep[v] = dep[u] + 1;
      dfs(v, u);
      us[usLen++] = u;
    }
  }
  void build(int rt_) {
    assert(0 <= rt_); assert(rt_ < n);
    rt = rt_;
    par.assign(n, -1);
    dep.assign(n, -1);
    su.assign(n, -1);
    usLen = 0;
    us.assign(2 * n - 1, -1);
    dep[rt] = 0;
    dfs(rt, -1);
    assert(usLen == 2 * n - 1);
    const int l = (31 - __builtin_clz(usLen)) + 1;
    buffer.resize(l * usLen);
    mn.resize(l);
    for (int e = 0; e < l; ++e) mn[e] = buffer.data() + e * usLen;
    for (int j = 0; j < usLen; ++j) mn[0][j] = us[j];
    for (int e = 0; e < l - 1; ++e) for (int i = 0; i + (1 << (e + 1)) <= usLen; ++i) {
      mn[e + 1][i] = shallower(mn[e][i], mn[e][i + (1 << e)]);
    }
  }

  int shallower(int u, int v) const {
    return (dep[u] <= dep[v]) ? u : v;
  }
  int operator()(int u, int v) const {
    int j0 = su[u], j1 = su[v];
    if (j0 > j1) swap(j0, j1);
    ++j1;
    const int e = 31 - __builtin_clz(j1 - j0);
    return shallower(mn[e][j0], mn[e][j1 - (1 << e)]);
  }
  int dist(int u, int v) const {
    return dep[u] + dep[v] - 2 * dep[operator()(u, v)];
  }
};

////////////////////////////////////////////////////////////////////////////////


struct Tree {
  int n;
  // vector<vector<pair<int, int>>> graph;
  vector<pair<int, pair<int, int>>> edges;
  // explicit Tree(int n_) : n(n_), graph(n) {}
  explicit Tree(int n_) : n(n_), edges() {
    edges.reserve(n - 1);
  }
  void ae(int u, int v, int c) {
    // graph[u].emplace_back(c, v);
    // graph[v].emplace_back(c, u);
    edges.emplace_back(c, make_pair(u, v));
  }
  
  vector<int> pt;
  vector<pair<int, int>> zu;
  void build() {
    pt.assign(n + 1, 0);
    for (int i = 0; i < n - 1; ++i) {
      const int u = edges[i].second.first;
      const int v = edges[i].second.second;
      ++pt[u];
      ++pt[v];
    }
    for (int u = 0; u < n; ++u) pt[u + 1] += pt[u];
    zu.resize(2 * (n - 1));
    for (int i = n - 1; --i >= 0; ) {
      const int c = edges[i].first;
      const int u = edges[i].second.first;
      const int v = edges[i].second.second;
      zu[--pt[u]] = make_pair(c, v);
      zu[--pt[v]] = make_pair(c, u);
    }
  }
  
  template <class F> void decomp(F f) {
    sz.assign(n, 0);
    dfsSz(0, -1);
    del.assign(n, 0);
    solveRec(0, f);
  }
  vector<int> sz, del;
  void dfsSz(int u, int p) {
    sz[u] = 1;
    // for (const auto &e : graph[u]) { const int v = e.second; if (p != v) {
    for (int j = pt[u]; j < pt[u + 1]; ++j) { const auto &e = zu[j]; const int v = e.second; if (p != v) {
      dfsSz(v, u);
      sz[u] += sz[v];
    }}
  }
  template <class F> void solveRec(int u, F f) {
    for (; ; ) {
      int vm = -1;
      // for (const auto &e : graph[u]) { const int v = e.second; if (!del[v]) {
      for (int j = pt[u]; j < pt[u + 1]; ++j) { const auto &e = zu[j]; const int v = e.second; if (!del[v]) {
        if (!~vm || sz[vm] < sz[v]) {
          vm = v;
        }
      }}
      if (!~vm || 2 * sz[vm] <= sz[u]) {
        solveSubtree(u, f);
        del[u] = 1;
        // for (const auto &e : graph[u]) { const int v = e.second; if (!del[v]) {
        for (int j = pt[u]; j < pt[u + 1]; ++j) { const auto &e = zu[j]; const int v = e.second; if (!del[v]) {
          solveRec(v, f);
        }}
        break;
      } else {
        sz[u] -= sz[vm];
        sz[vm] += sz[u];
        u = vm;
      }
    }
  }
  template <class F> void solveSubtree(int r, F f) {
    int allLen = 0;
    vector<pair<int, int>> all(sz[r]);
    all[allLen++] = make_pair(0, r);
    // for (const auto &e1 : graph[r]) { const int r1 = e1.second; if (!del[r1]) {
    for (int j1 = pt[r]; j1 < pt[r + 1]; ++j1) { const auto &e1 = zu[j1]; const int r1 = e1.second; if (!del[r1]) {
      int queLen = 0;
      // vector<pair<int, int>> que(sz[r1]);
      auto *que = all.data() + allLen;
      que[queLen++] = e1;
      for (int k = 0; k < sz[r1]; ++k) {
        const int d = que[k].first;
        const int u = que[k].second;
        // for (const auto &e : graph[u]) { const int v = e.second; if (!del[v] && sz[u] > sz[v]) {
        for (int j = pt[u]; j < pt[u + 1]; ++j) { const auto &e = zu[j]; const int v = e.second; if (!del[v] && sz[u] > sz[v]) {
          que[queLen++] = make_pair(d + e.first, v);
        }}
      }
      // f(-1, que);
      f(-1, que, que + queLen);
      // for (int k = 0; k < sz[r1]; ++k) all[allLen++] = que[k];
      allLen += queLen;
    }}
    // f(+1, all);
    f(+1, all.data(), all.data() + allLen);
  }
};


int N;
vector<int> A[2], B[2];

int main() {
  for (; ~scanf("%d", &N); ) {
    for (int h = 0; h < 2; ++h) {
      A[h].resize(N - 1);
      B[h].resize(N - 1);
      for (int i = 0; i < N - 1; ++i) {
        scanf("%d%d", &A[h][i], &B[h][i]);
        --A[h][i];
        --B[h][i];
      }
    }
    
    Hld hld[2];
    for (int h = 0; h < 2; ++h) {
      hld[h] = Hld(N);
      for (int i = 0; i < N - 1; ++i) hld[h].ae(A[h][i], B[h][i]);
      hld[h].build(0);
// cerr<<hld[h]<<endl;
    }
    
    Lca L1(N);
    for (int i = 0; i < N - 1; ++i) L1.ae(A[1][i], B[1][i]);
    L1.build(0);
    
    unsigned long long ans = 0;
    vector<int> ds(N, -1);
    
    Tree T0(N);
    for (int i = 0; i < N - 1; ++i) T0.ae(A[0][i], B[0][i], 1);
    T0.build();
    // T0.decomp([&](int s0, const vector<pair<int, int>> &fs) -> void {
    T0.decomp([&](int s0, const pair<int, int> *fL, const pair<int, int> *fR) -> void {
      const vector<pair<int, int>> fs(fL, fR);
// cerr<<"s0 = "<<s0<<", fs = "<<fs<<endl;
      const int fsLen = fs.size();
      if (fsLen <= 100) {
        unsigned long long here = 0;
        for (int k = 0; k < fsLen; ++k) for (int l = k + 1; l < fsLen; ++l) {
          const int u = fs[k].second;
          const int v = fs[l].second;
          here += (unsigned long long)(fs[k].first + fs[l].first) * L1.dist(u, v);
        }
        ans += s0 * here;
        return;
      }
      vector<int> us(fsLen);
      for (int k = 0; k < fsLen; ++k) us[k] = fs[k].second;
      const auto vsps = hld[1].compress(us);
      const auto &vs = vsps.first;
      const auto &ps = vsps.second;
      const int n = vs.size();
      for (int k = 0; k < fsLen; ++k) ds[hld[1].ids[us[k]]] = fs[k].first;
      Tree T1(n);
      for (int y = 1; y < n; ++y) {
        const int x = ps[y];
        T1.ae(x, y, hld[1].dep[vs[y]] - hld[1].dep[vs[x]]);
      }
      T1.build();
      // T1.decomp([&](int s1, const vector<pair<int, int>> &gs) -> void {
      T1.decomp([&](int s1, const pair<int, int> *gL, const pair<int, int> *gR) -> void {
// cerr<<"  s1 = "<<s1<<", gs = "<<gs<<endl;
        unsigned long long sum = 0, sum0 = 0, sum1 = 0, sum01 = 0;
        // for (const auto &g : gs) {
          // const int x = g.second;
          // const int d0 = ds[x];
          // const int d1 = g.first;
        for (const auto *g = gL; g != gR; ++g) {
          const int x = g->second;
          const int d0 = ds[x];
          const int d1 = g->first;
          if (~d0) {
            sum += 1;
            sum0 += d0;
            sum1 += d1;
            sum01 += (unsigned long long)d0 * d1;
          }
        }
        unsigned long long here = 0;
        here += sum * sum01;
        here += sum0 * sum1;
        ans += s0 * s1 * here;
      });
      for (int k = 0; k < fsLen; ++k) ds[hld[1].ids[us[k]]] = -1;
    });
    
    ans *= 2;
    printf("%llu\n", ans);
    
#ifdef LOCAL
if(N<=1000){
 unsigned long long brt=0;
 for(int u=0;u<N;++u)for(int v=0;v<N;++v){
  unsigned long long d[2];
  for(int h=0;h<2;++h){
   const int l=hld[h].lca(u,v);
   d[h]=hld[h].dep[u]+hld[h].dep[v]-2*hld[h].dep[l];
  }
  brt+=d[0]*d[1];
 }
 if(brt!=ans){
  cerr<<N<<endl;
  for(int h=0;h<2;++h)for(int i=0;i<N-1;++i)cerr<<(A[h][i]+1)<<" "<<(B[h][i]+1)<<endl;
  cerr<<"brt = "<<brt<<endl;
  cerr<<"ans = "<<ans<<endl;
  assert(false);
 }
}
#endif
  }
  return 0;
}