#include<bits/stdc++.h>
#include<atcoder/all>
#define chmin(x,y) (x) = min((x),(y))
#define chmax(x,y) (x) = max((x),(y))
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define vec vector
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define pb push_back 
#define eb emplace_back

using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;
const ll mod = 998244353;
using mint = modint998244353;
const vector<int> dx = {1,0,-1,0}, dy = {0,1,0,-1};
// using Graph = vector<vector<pair<int,ll>>>;
using Graph = vector<vector<int>>;

int main(){
  // input + prep
  int N;
  cin >> N;
  vec<int> S(N+2,0); // 超頂点：0=start, N+1=end
  rep(i,N) cin >> S[i+1];
  Graph G(N+2);
  rep(i,N-1){
    int a,b;
    cin >> a >> b;
    if(S[a] > S[b]) G[b].pb(a);
    if(S[a] < S[b]) G[a].pb(b);
  }
  rep(i,N){
    G[0].pb(i+1);
    G[i+1].pb(N+1);
  }
  
  // solve
  vec<ll> dist(N+2,-1);
  priority_queue<pair<ll,int>> pq;
  dist[0] = 0;
  pq.emplace(0,0);
  while(!pq.empty()){
    auto[score, pos] = pq.top();
    pq.pop();
    if(dist[pos] > score) continue;

    for(auto nxt : G[pos]){
      ll score_nxt = score + S[nxt];
      if(dist[nxt] < score_nxt){
        dist[nxt] = score_nxt;
        pq.emplace(score_nxt, nxt);
      }
    }
  }
  
  // output
  ll ans = dist.back();
  cout << ans << endl;
}