#include <bits/stdc++.h>
using namespace std;
#define int long long

void QAQ() {
    int n, m;
    cin >> n >> m;

    vector<int> a(n + 1);

    for (int i = 1; i <= n; i++) {
        cin >> a[i];
    }

    vector adj(n + 1, set<int>());

    for (int i = 1, u, v; i <= m; i++) {
        cin >> u >> v;
        adj[u].emplace(v), adj[v].emplace(u);
    }

    vector<int> dp(n + 1);
    int ans = 0;

    for (int i = 1; i <= n; i++) {
        if (adj[i].size() != 1) {
            ans = max(ans, a[i]);
        } else {
            dp[i] = a[i];
        }
    }

    vector<int> vis(n + 1);

    auto dfs = [&](auto && self, int u, int fa = 0) -> void {
        multiset<int, greater<>> s;
        vis[u] = 1;
        for (auto & v : adj[u]) if (v != fa && !vis[v]) {
            self(self, v, u);
            if (dp[v]) {
                s.insert(dp[v]);
            }
        }
        if (s.size() >= 3) {
            ans = max(ans, *next(s.begin()));
        } else if (s.size() >= 2) {
            // if (adj[u].size() > 2) {
                ans = max(ans, *next(s.begin()));
            // }
            dp[u] = *next(s.begin());
        } else {
            
        }
    };

    for (int i = 1; i <= n; i++) {
        if (adj[i].size() >= 2) {
            dfs(dfs, i);
            break;
        }
    }

    cout << ans << "\n";
}

signed main() {
    cin.tie(0) -> sync_with_stdio(0);
    int t = 1;
    // cin >> t;
    for(cout << fixed << setprecision(12); t--; QAQ());
}