#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define endl "\n"
#define all(aa) aa.begin(), aa.end()
int main(){
int n, m;
cin>>n>>m;
vector<int> v(n);
vector<vector<int>> g(n);
for(auto &e:v) cin>>e;
for(int i=0; i<m; i++){
int a, b;
cin>>a>>b;
a--; b--;
g[a].push_back(b);
g[b].push_back(a);
}
vector<int> ans(n, -1), ans2(n, -1);
priority_queue<pair<int, int>> pq;
pq.push({0, 0});
while(pq.size()){
auto [t, cur]=pq.top();
pq.pop();
if(ans[cur]!=-1) continue;
t=ans[cur]=-t;
for(auto ch:g[cur]){
pq.push({-max(t, v[ch]), ch});
}
}
pq.push({0, n-1});
while(pq.size()){
auto [t, cur]=pq.top();
pq.pop();
if(ans2[cur]!=-1) continue;
t=ans2[cur]=-t;
for(auto ch:g[cur]){
pq.push({-max(t, v[ch]), ch});
}
}
int res=INT_MAX;
for(int i=0; i<n; i++){
res=min(res, max(ans[i], ans2[i])*2);
}
cout<<res<<endl;
}
