#include <bits/stdc++.h>
#define L(i, j, k) for(int i = (j); i <= (k); i++)
#define R(i, j, k) for(int i = (j); i >= (k); i--)
#define ll long long
#define sz(a) ((int) a.size())
#define all(a) a.begin(), a.end()
#define vi vector<ll>
#define pb emplace_back
#define me(a, x) memset(a, x, sizeof(a))
#define fst first
#define snd second
#define ii pair<int, int>
using namespace std;
const int MAXN=2e5+5,LOG=20,INF=1e9;
ll lnk[MAXN],tam[MAXN],bst[MAXN],ans[MAXN],dist[MAXN],dist2[MAXN],up[MAXN][LOG],n;
ll val[MAXN];
vi adj[MAXN],adjr[MAXN];
bool lib[MAXN];
int jump(int a,ll k){
L(i,0,LOG-1){
if((1ll<<i)&k)a=up[a][i];
}
return a;
}
int lca(int a,int b){
if(dist[a]<dist[b])swap(a,b);
a=jump(a,dist[a]-dist[b]);
if(a==b)return a;
R(i,LOG-1,0){
if(up[a][i]!=up[b][i]){
a=up[a][i];
b=up[b][i];
}
}
return up[a][0];
}
void dfs(int u,int par,int d=0){
dist[u]=d;
for(auto v:adj[u]){
if(v==par)continue;
up[v][0]=u;
dfs(v,u,d+1);
}
}
int find(int a){
while(lnk[a]!=a)a=lnk[a];
return a;
}
void dsu(int a,int b){
a=find(a),b=find(b);
assert(a!=b);
if(tam[a]<tam[b])swap(a,b);
lnk[b]=a;
tam[a]+=tam[b];
adjr[bst[a]].pb(bst[b]);
adjr[bst[b]].pb(bst[a]);
if(val[bst[a]]<val[bst[b]])bst[a]=bst[b];
}
ll getDistance(int a,int b){
return dist[a]+dist[b]-dist[lca(a,b)]*2;
}
signed int main(){
ios::sync_with_stdio(false);
cin.tie(nullptr);
cin>>n;
vector<ii>p;
L(i,1,n){
tam[i]=1;
ans[i]=0;
cin>>val[i];
p.pb(val[i],i);
bst[i]=i;
lnk[i]=i;
}
L(i,0,n-2){
int a,b;cin>>a>>b;
adj[a].pb(b);
adj[b].pb(a);
}
dfs(1,-1);
//~ cout<<"PASS"<<endl;
L(i,1,LOG-1){
L(j,1,n){
up[j][i]=up[up[j][i-1]][i-1];
}
}
sort(all(p));
L(i,0,n-1){
lib[p[i].snd]=1;
for(int v:adj[p[i].snd]){
if(!lib[v])continue;
//~ cout<<p[i].snd<<" "<<v<<endl;
dsu(p[i].snd,v);
}
}
//~ cout<<"PASS2"<<endl;
queue<int>q;
q.push(p[n-1].snd);
//~ cout<<p[n].snd<<endl;
L(i,1,n)dist2[i]=-INF;
dist2[p[n-1].snd]=0;
while(sz(q)){
int u=q.front();q.pop();
//~ cout<<u<<endl;
for(int v:adjr[u]){
//~ cout<<v<<endl;
if(dist2[v]!=-INF)continue;
dist2[v]=dist2[u]+getDistance(u,v);
q.push(v);
}
}
cout<<*max_element(dist2+1,dist2+n+1)<<endl;
}
