#include <bits/stdc++.h>
using namespace std;

vector<int> graph[100010];
vector<int> tree[100010];

int mas[100010];
int n;

bool used[100010] = {};
void makeTree(int m){
  used[m] = true;
  for(int i = 0;i < graph[m].size();i++){
    if(!used[graph[m][i]]){
      tree[m].push_back(graph[m][i]);
      makeTree(graph[m][i]);
    }
  }
  return;
}

int dp[100010] = {};
int ep[100010] = {};
int fp[100010] = {};

void dfs(int x){
  dp[x] = mas[x];
  ep[x] = 0;
  fp[x] = 0;

  if(tree[x].size() == 0) return;

  for(int i = 0;i < tree[x].size();i++){
    dfs(tree[x][i]);
  }

  //bool used[100010] = {};
  memset(used,false,sizeof(used));
  for(int i = 0;i < tree[x].size();i++){
    if(dp[tree[x][i]] - 2 >= 0){
      used[tree[x][i]] = true;
      dp[x] += dp[tree[x][i]] - 2;
    }
  }

  int kari = 0;
  int kari2 = 0;
  for(int i = 0;i < tree[x].size();i++){
    if(used[tree[x][i]]){
      if(ep[tree[x][i]]+1 > kari){
        kari2 = kari;
        kari = ep[tree[x][i]]+1;
      }else if(ep[tree[x][i]]+1 > kari2){
        kari2 = ep[tree[x][i]]+1;
      }
    }else{
      if(ep[tree[x][i]]+1+dp[tree[x][i]]-2 > kari){
        kari2 = kari;
        kari = ep[tree[x][i]]+1+dp[tree[x][i]]-2;
      }else if(ep[tree[x][i]]+1+dp[tree[x][i]]-2 > kari2){
        kari2 = ep[tree[x][i]]+1+dp[tree[x][i]]-2;
      }
    }
  }

  if(kari >= 0){
    ep[x] = kari;
  }

  int kari3 = 0;
  for(int i = 0;i < tree[x].size();i++){
    if(used[tree[x][i]]){
      kari3 = max(kari3,fp[tree[x][i]]);
    }else{
      kari3 = max(kari3,fp[tree[x][i]]+dp[tree[x][i]]-2);
    }
  }

  fp[x] = max(kari3,max(kari+kari2,max(kari,kari2)));
  return;
}


int main(){
  cin >> n;
  for(int i = 0;i < n;i++){
    cin >> mas[i];
  }

  int a, b;
  for(int i = 0;i < n-1;i++){
    cin >> a >> b;
    a--; b--;
    graph[a].push_back(b);
    graph[b].push_back(a);
  }

  makeTree(0);
  dfs(0);

  int ans = INT_MIN;
  for(int i = 0;i < n;i++){
    ans = max(ans,dp[i]+fp[i]);
  }

  cout << ans << endl;

  return 0;
}

