import sys
import math
#from collections import deque, defaultdict, Counter
#import heapq
#import bisect
#import itertools
#import functools

# 外部ライブラリ（AtCoder環境で利用可能）
#from sortedcontainers import SortedList, SortedSet, SortedDict
#from atcoder.dsu import DSU
#from atcoder.segtree import SegTree
#from atcoder.lazysegtree import LazySegTree
#from atcoder.fenwicktree import FenwickTree

# 入力高速化
#input = sys.stdin.readline
# 再帰回数上限
sys.setrecursionlimit(500000)
# よくあるmod
#MOD = 1000000007
MOD = 998244353

def solve():
    # 解答ここから
    N = int(input())
    S = list(map(int, input().split(' ')))
    G = {u: [] for u in range(N)}
    for _ in range(N-1):
        u, v = map(int, input().split(' '))
        u-=1
        v-=1
        G[u].append(v)
        G[v].append(u)
    visited = [False] * N
    def dfs(u, ans):
        inc = 0
        dec = 0
        for v in G[u]:
            if visited[v]: continue
            visited[v] = True
            a, i, d = dfs(v, ans)
            ans = max(a, ans)
            if S[u] < S[v]:
                dec = max(dec, d + S[v])
            elif S[u] > S[v]:
                inc = max(inc, i + S[v])
            ans = max(ans, a)
        ans = max(ans, inc + dec + S[u])
        return ans, inc, dec
    visited[0] = True
    print(dfs(0, 0)[0])


            
        
if __name__ == '__main__':
    T = 1
    for _ in range(T):
        solve()