n = read_line.to_i
s = read_line.split.map(&.to_i64)
g = Array.new(n) { [] of Int32 }
(n - 1).times do
  a, b = read_line.split.map(&.to_i)
  g[a - 1] << b - 1
  g[b - 1] << a - 1
end
q = [0]
parent = Array.new(n, -1)
n.times do |i|
  cur = q[i]
  g[cur].each do |adj|
    next if parent[cur] == adj
    parent[adj] = cur
    q << adj
  end
end

dp0 = Array.new(n, 0i64)
dp1 = Array.new(n, 0i64)

# bottom -> top
(n - 1).downto(0) do |i|
  cur = q[i]
  par = parent[cur]
  dp0[cur] = s[cur]
  dp1[cur] = s[cur]
  g[cur].each do |adj|
    next if par == adj
    if s[adj] < s[cur]
      dp0[cur] = {dp0[cur], dp0[adj] + s[cur]}.max
    elsif s[adj] > s[cur]
      dp1[cur] = {dp1[cur], dp1[adj] + s[cur]}.max
    end
  end
end

puts n.times.max_of { |i| dp0[i] + dp1[i] - s[i] }