#include <iostream>
#include <algorithm>
#include <cstring>
#include <vector>
#include <set>
#include <stack>
using namespace std;
typedef long long ll;
const int maxn = 1e5 + 10;
vector<int> graph[maxn];
int experience[maxn];
ll dp1[maxn], dp2[maxn];

void dfs(int node, int prev) {
    ll sum = 0;
    for(int i = 0; i < (int) graph[node].size(); i++) {
        int neighbour = graph[node][i];
        if(neighbour == prev) continue;

        dfs(neighbour, node);
        sum += max(dp1[neighbour], dp2[neighbour]);
    }
    dp1[node] = sum;
    dp2[node] = sum;
    for(int i = 0; i < (int) graph[node].size(); i++) {
        int neighbour = graph[node][i];
        if(neighbour == prev) continue;

        if(experience[node] > experience[neighbour]) {
            dp1[node] = max(dp1[node], sum - max(dp1[neighbour], dp2[neighbour]) + abs(experience[neighbour] - experience[node]) + dp1[neighbour]);
        }
        else {
            dp2[node] = max(dp2[node], sum - max(dp1[neighbour], dp2[neighbour]) + abs(experience[neighbour] - experience[node]) + dp2[neighbour]);
        }

    }

}
int main() {
    ios_base::sync_with_stdio(false);
    int n;
    cin >> n;

    for(int i = 0; i < n; i++) {
        cin >> experience[i];
    }
    for(int i = 1; i < n; i++) {
        int a, b;
        cin >> a >> b;
        a--; b--;
        graph[a].push_back(b);
        graph[b].push_back(a);
    }
    dfs(0, -1);
    cout << max(dp1[0], dp2[0]) << endl;
    return 0;
}