#include<bits/stdc++.h>
using namespace std;
using ll=long long;
const int N=1e5+10;
ll a[N];
ll d[N];
int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n,m; cin>>n>>m;
    for(int i=1;i<=n;i++) cin>>a[i];
    for(int i=1;i<=m;i++){
        int u,v; cin>>u>>v;
        d[u]++;
        d[v]++;
    }
    if(n==1){
        cout<<a[1]<<"\n";
        return 0;
    }
    ll mx=-1,ans1=-1,ans2=-1;
    for(int i=1;i<=n;i++){
        if(d[i]==1){
            if(a[i]>ans1){
                ans2=ans1;
                ans1=a[i];
            }
            else ans2=max(ans2,a[i]);
        }
        else mx=max(mx,a[i]);
    }
    if(ans2==-1) cout<<mx;
    else if(mx=-1) cout<<ans2;
    else cout<<max(mx,ans2);
}