#include<bits/stdc++.h>
using namespace std;
#define int long long
#define pii pair<int, int>
int n;
const int MAX_N = 5000;
vector<int> adj[MAX_N];
int H[MAX_N];
int score[MAX_N];
struct DSU{
vector<int> dsu;
vector<int> sz;
vector<pair<int, pii>> max_v;
DSU(int len){
dsu.resize(len);
sz.resize(len);
max_v.resize(len);
for(int i = 0; i<len; i++){
dsu[i] =i;
sz[i]= 1;
max_v[i] = {H[i], {i, 0}};
}
}
int getC(int a){
if(dsu[a] == a){
return a;
}
int b= getC(dsu[a]);
dsu[a] = b;
return b;
}
void merge(int a, int b){
a=getC(a);
b=getC(b);
if(sz[a]<sz[b]){
swap(a, b);
}
dsu[b] = a;
sz[a] += sz[b];
if(max_v[a].first<max_v[b].first){
max_v[a] = max_v[b];
}
}
};
signed main(){
cin>>n;
vector<pii> pts;
for(int i = 0; i<n; i++){
cin>>H[i];
pts.push_back({H[i], i});
}
for(int i = 0; i<n-1; i++){
int a, b;
cin>>a>>b;
adj[a-1].push_back(b-1);
adj[b-1].push_back(a-1);
}
sort(pts.begin(), pts.end());
DSU dsu =DSU(n);
for(int i = 0; i<n; i++){
int u = pts[i].second;
int s_after = 0;
for(auto v: adj[u]){
if(H[v]<H[u]){
//cout<<v<<" score "<<dsu.max_v[dsu.getC(v)].first<<" "<<dsu.max_v[dsu.getC(v)].second.first<<" "<<dsu.max_v[dsu.getC(v)].second.second<<endl;
s_after = max(s_after, dsu.max_v[dsu.getC(v)].second.second + abs(u-dsu.max_v[dsu.getC(v)].second.first));
//cout<<"merge "<<u<<" "<<v<<endl;
dsu.merge(u, v);
}
}
dsu.max_v[dsu.getC(u)] = {H[u],{u, s_after}};
//cout<<u<<" "<<score[u]<<endl;
}
cout<<dsu.max_v[dsu.getC(0)].second.second<<endl;
}
