#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
//#include<bits/extc++.h>
//__gnu_pbds
const int N = 200005;
int w[N];
vector<int> side[N];
vector<int> from[N];
int head[N];
int p[N][19];
int dep[N];
ll dp[N];
void dfs(int cur){
for(auto v : side[cur]){
if(v==p[cur][0]) continue;
p[v][0]=cur;
dep[v]=dep[cur]+1;
dfs(v);
}
}
int dis(int a,int b){
int oga= a;
int ogb = b;
if(dep[a]>dep[b]) swap(a,b);
for(int l = 18;l>=0;l--){
if(dep[p[b][l]]>dep[a]) b = p[b][l];
}
if(dep[b]!=dep[a]) b = p[b][0];
if(a==b){
return abs(dep[oga]-dep[ogb]);
}
for(int l=18;l>=0;l--){
if(p[b][l]!=p[a][l]){
a = p[a][l];
b = p[b][l];
}
}
if(a!=b) a=p[a][0];
return abs(dep[a]-dep[oga])+abs(dep[a]-dep[ogb]);
}
int query(int a){
if(head[a]==a) return a;
head[a] = query(head[a]);
return head[a];
}
void join(int a,int b){
a = query(a);b = query(b);
if(a==b) return;
if(w[a]>w[b]) swap(a,b);
head[a] =b;
}
int main(){
ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0);
int n;cin>>n;
for(int i=1;i<=n;i++) cin>>w[i];
for(int i=0;i<n-1;i++){
int a,b;cin>>a>>b;
side[a].push_back(b);
side[b].push_back(a);
}
p[1][0]=1;
dep[1]=1;
dfs(1);
for(int l=1;l<19;l++){
for(int i=1;i<=n;i++){
p[i][l] = p[p[i][l-1]][l-1];
}
}
int order[n];
for(int i=1;i<=n;i++) {order[i-1]=i;head[i]=i;}
sort(order,order+n,[&](const int a,const int b){return w[a]<w[b];});
for(int i=0;i<n;i++){
int cur = order[i];
for(auto v : side[cur]){
if(w[v]>w[cur]) continue;
int g = query(v);
from[g].push_back(cur);
join(g,cur);
}
}
sort(order,order+n,[&](const int a,const int b){return w[a]>w[b];});
ll maxn = 0;
for(int i=1;i<n;i++){
int cur = order[i];
for(auto v : from[cur]){
dp[cur] = max(dp[v]+dis(v,cur),dp[cur]);
}
maxn = max(dp[cur],maxn);
}
cout<<maxn<<"\n";
return 0;
}
