#include <bits/stdc++.h>
using namespace std;
#define forn(i,n) for(int i=0;i<int(n);i++)
#define forsn(i,s,n) for(int i=int(s);i<int(n);i++)
#define dforn(i,n) for(int i=int(n)-1;i>=0;i--)
#define dforsn(i,s,n) for(int i=int(n)-1;i>=int(s);i--)
#define fst first
#define snd second
#define pb push_back
#define eb emplace_back
#define sz(x) (int)x.size()
#define all(x) x.begin(), x.end()
typedef long long ll;
typedef vector<ll> vll;
typedef vector<int> vi;
typedef pair<int,int> ii;
const ll INF=1e18;
pair<vll,vll> dijkstra(int s, vector<vi> &adj, vi &a){
int n=sz(adj);
vll dist(n,INF);
vll height(n,INF);
priority_queue<tuple<ll,int,int>> pq;
pq.emplace(0,0,s);
dist[s]=0,height[s]=0;
vector<bool> vis(n,false);
while(!pq.empty()){
auto[d,h,u]=pq.top();
pq.pop();
for(int v:adj[u]){
ll newH=max(h,a[v]);
ll newD=max(dist[u]+1,newH);
if(make_pair(-newD,-newH)>make_pair(-dist[v],-height[v])){
dist[v]=newD,height[v]=newH;
pq.emplace(-dist[v],-height[v],v);
}
}
}
return {dist,height};
}
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
int n,m;
cin>>n>>m;
vi a(n);
forn(i,n) cin>>a[i];
vector<vi> adj(n);
forn(i,m){
int u,v;
cin>>u>>v;
--u,--v;
adj[u].pb(v);
adj[v].pb(u);
}
auto[distFromS,heightFromS]=dijkstra(0,adj,a);
auto[distToT,heightToT]=dijkstra(n-1,adj,a);
ll res=INF;
forn(u,n){
ll curr=2*max(distFromS[u],distToT[u]);
res=min(res,curr);
for(int v:adj[u]){
curr=2*max(distFromS[u],distToT[v])+1;
res=min(res,curr);
}
}
cout<<res<<'\n';
return 0;
}
