#include <bits/stdc++.h>
using namespace std;
#define int int64_t
const int maxn = 200001;
const int maxlogn = 19;
vector<int> g[maxn];
int h[maxn];
int p[maxn];
pair<int,int> mp[maxn];
int dp[maxn];
int pp[maxn];
int la[maxlogn][maxn];
int d[maxn];
int tin[maxn],tout[maxn];
int times = 0;
int get(int v)
{
if(p[v] == v)
return v;
else
return p[v] = get(p[v]);
}
void unio(int u,int v)
{
u = get(u);
v = get(v);
if(u == v)
return ;
mp[v] = max(mp[u],mp[v]);
p[u] = v;
return ;
}
void dfs(int v,int pf,int dd)
{
tin[v] = times++;
pp[v] = pf;
d[v] = dd;
for(auto u:g[v])
{
if(u != pf)
dfs(u,v,dd+1);
}
tout[v] = times++;
return ;
}
int lp(int a,int b)
{
int a2 = a;
for(int i = maxlogn-1;i >= 0;--i)
{
//if(i == 0)
// {
// cout << la[i][a] << ' ';
// }
if(tin[la[i][a]] > tin[b] || tout[la[i][a]] < tout[b])
{
a = la[i][a];
}
}
// cout << a << ' ';
if(tin[a] > tin[b] || tout[a] < tout[b])
{
a = pp[a];
}
// cout << a2 << ' ' << b << ' ' << a << "\n";
return d[a2] + d[b] - 2*d[a];
}
signed main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
int n;
cin >> n;
for(int i = 0;i < n;++i)
{
cin >> h[i];
}
for(int i = 0;i < n-1;++i)
{
int u,v;
cin >> u >> v;
u--;
v--;
g[u].push_back(v);
g[v].push_back(u);
}
dfs(0,0,0);
for(int i = 0;i < maxlogn;++i)
{
for(int j = 0;j < n;++j)
{
if(i == 0)
la[i][j] = pp[j];
else
la[i][j] = la[i-1][la[i-1][j]];
}
}
vector<int> ind(n);
vector<bool> en(n);
for(int j = 0;j < n;++j)
{
p[j] = j;
mp[j] = {h[j],j};
ind[j] = j;
en[j] = 0;
}
sort(ind.begin(),ind.end(),[&](int a,int b){return h[a] < h[b];});
for(int j = 0;j < n;++j)
{
int v = ind[j];
en[v] = 1;
dp[v] = 0;
for(auto u:g[v])
{
if(en[u])
{
int tv = mp[get(u)].second;
// cout << tv << ' ' << dp[tv] << ' ' << v << ' ' << lp(v,tv);
dp[v] = max(dp[v],dp[tv] + lp(v,tv));
}
}
for(auto u:g[v])
{
if(en[u])
{
unio(v,u);
}
}
// cout << dp[v] << "!\n";
if(j == n-1)
cout << dp[v] << "\n";
}
}
