#include <bits/stdc++.h>
using namespace std;
/// 123
static const int N = 1e6 + 10;
class lca_t {
public:
int rmq[20][N * 2];
int pos[N], d[N];
vector<int> adj[N];
int timer;
int n;
lca_t(int n = 0) : n(n) {}
void add_edge(int u, int v) {
adj[u].emplace_back(v);
adj[v].emplace_back(u);
}
void dfs(int u, int p) {
rmq[0][timer++] = u;
for (int v : adj[u]) {
if (v == p) continue;
d[v] = d[u] + 1;
dfs(v, u);
rmq[0][timer++] = u;
}
}
void build(int root) {
timer = 0;
d[root] = 0;
dfs(root, -1);
for (int i = 0; i < timer; i++) pos[rmq[0][i]] = i;
assert(__lg(timer) < 20);
for (int i = 1; i <= __lg(timer); i++) {
for (int j = 0; j + (1 << i) <= timer; j++) {
rmq[i][j] = d[rmq[i - 1][j]] < d[rmq[i - 1][j + (1 << (i - 1))]]
? rmq[i - 1][j]
: rmq[i - 1][j + (1 << (i - 1))];
}
}
}
int get(int u, int v) {
int l = pos[u], r = pos[v];
if (l > r) swap(l, r);
int i = __lg(r - l + 1);
r -= (1 << i) - 1;
int x = d[rmq[i][l]] < d[rmq[i][r]] ? rmq[i][l] : rmq[i][r];
return d[u] + d[v] - d[x] * 2;
}
} lca;
int32_t main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
int n;
cin >> n;
vector<int> a(n);
for (int i = 0; i < n; i++) cin >> a[i];
vector<vector<int>> adj(n);
lca = lca_t(n);
for (int i = 0; i < n - 1; i++) {
int u, v;
cin >> u >> v;
u--, v--;
if (a[u] < a[v]) swap(u, v);
adj[u].emplace_back(v);
lca.add_edge(u, v);
}
vector<int> ord(n);
iota(ord.begin(), ord.end(), 0);
sort(ord.begin(), ord.end(), [&](int i, int j) {
return a[i] < a[j];
});
lca.build(0);
vector<int> par(n, -1), m(n, -1);
vector<int64_t> f(n, 0);
for (int i = 0; i < n; i++) m[i] = i;
function<int(int)> root = [&](int u) { return par[u] < 0 ? u : (par[u] = root(par[u])); };
function<void(int, int)> unite = [&](int u, int v) {
u = root(u), v = root(v);
if (a[m[u]] < a[m[v]]) swap(u, v);
int64_t ff = max(f[u], f[v] + lca.get(m[u], m[v]));
if (par[u] > par[v]) swap(u, v);
if (a[m[u]] < a[m[v]]) m[u] = m[v];
par[u] += par[v];
par[v] = u;
f[u] = ff;
};
for (int i : ord) {
for (int j : adj[i]) unite(i, j);
}
cout << f[root(0)];
}
