#include <bits/stdc++.h>
using namespace std;
template <typename T>
void read(T &x) {
  x = 0;
  char ch = getchar();
  long long f = 1;
  while (!isdigit(ch)) {
    if (ch == '-') f *= -1;
    ch = getchar();
  }
  while (isdigit(ch)) {
    x = x * 10 + ch - 48;
    ch = getchar();
  }
  x *= f;
}
template <typename T, typename... Args>
void read(T &first, Args &...args) {
  read(first);
  read(args...);
}
template <typename T>
void write(T arg) {
  T x = arg;
  if (x < 0) {
    putchar('-');
    x = -x;
  }
  if (x > 9) {
    write(x / 10);
  }
  putchar(x % 10 + '0');
}
template <typename T, typename... Ts>
void write(T arg, Ts... args) {
  write(arg);
  if (sizeof...(args) != 0) {
    putchar(' ');
    write(args...);
  }
}
using namespace std;
long long gcd(long long a, long long b) { return b == 0 ? a : gcd(b, a % b); }
long long lcm(long long a, long long b) { return a / gcd(a, b) * b; }
int n;
const int N = 300005;
int a[N], maxn;
map<int, int> ma;
vector<int> edge[N];
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  maxn = -0x3f3f3f3f;
  for (int i = 1; i <= n; i++) {
    cin >> a[i];
    ma[a[i]]++;
    maxn = max(a[i], maxn);
  }
  for (int i = 1; i < n; i++) {
    int u, v;
    cin >> u >> v;
    edge[u].push_back(v);
    edge[v].push_back(u);
  }
  int ans = maxn + 2;
  for (int i = 1; i <= n; i++) {
    int ok = 0;
    for (auto v : edge[i]) {
      ma[a[v]]--;
      if (a[v] == maxn) ok = 1;
    }
    if (!ma[maxn]) ans = maxn + 1;
    if (a[i] == maxn && ma[maxn] == 1) {
      if (ma[maxn - 1] || ok)
        ans = maxn + 1;
      else {
        ans = maxn;
        break;
      }
    }
    for (auto v : edge[i]) ma[a[v]]++;
  }
  cout << ans << endl;
}
