#include <bits/stdc++.h>
using namespace std;
void solve() {
    int n, m; cin>> n>> m;
    vector<int> a(n), d(n);
    for (auto& i : a) cin>> i;
    while (m--) {
        int x, y; cin>> x>> y;x--, y--; 
        d[x]++, d[y]++;
    }
    if (n == 1) cout<< a[0];
    else {
        int ans = -1;
        for (int i = 0; i < n; i++) if (d[i] >= 2) ans = max(ans, a[i]);
        cout<< ans;
    }
    cout<< '\n';
}
int main() {
    cin.tie(0)->sync_with_stdio(0);
    // int T; cin>> T; while (T--) solve();
    solve();
}