#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#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; }


int N;
vector<Int> C;
vector<int> A, B;

vector<vector<int>> graph;

// * > * > * > * [> * < *]
Int bad;
using PQ = priority_queue<Int>;
PQ solve(int u, int p) {
  PQ ret;
  for (const int v : graph[u]) if (p != v) {
    PQ res = solve(v, u);
    if (ret.size() < res.size()) {
      swap(ret, res);
    }
    for (; !res.empty(); ) {
      const Int x = res.top(); res.pop();
      ret.push(x);
    }
  }
  Int c = C[u];
  for (; ; ) {
    if (!ret.empty() && c <= ret.top()) {
      const Int x1 = ret.top(); ret.pop();
      if (!ret.empty()) {
        const Int x2 = ret.top(); ret.pop();
        c = c - x1 + x2;
      } else {
        bad += (c - x1);
        break;
      }
    } else {
      ret.push(c);
      break;
    }
  }
  return ret;
}

int main() {
  for (; ~scanf("%d", &N); ) {
    C.resize(N);
    for (int u = 0; u < N; ++u) {
      scanf("%lld", &C[u]);
    }
    A.resize(N - 1);
    B.resize(N - 1);
    for (int i = 0; i < N - 1; ++i) {
      scanf("%d%d", &A[i], &B[i]);
      --A[i];
      --B[i];
    }
    
    graph.assign(N, {});
    for (int i = 0; i < N - 1; ++i) {
      graph[A[i]].push_back(B[i]);
      graph[B[i]].push_back(A[i]);
    }
    bad = 0;
    PQ res = solve(0, -1);
    Int ans = 0;
    Int sig = +1;
    for (; !res.empty(); ) {
      const Int x = res.top(); res.pop();
      ans += sig * x;
      sig = -sig;
    }
    ans += sig * bad;
    printf("%lld\n", ans);
  }
  return 0;
}