#include<bits/stdc++.h>
using namespace std;
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
#define int long long
typedef pair<int,int> pii;
typedef vector<pii> vii;
typedef vector<int> vi;
typedef vector<bool> vb;
#define FOR(i,a) for(int i=0;i<(a);i++)
#define FORE(i,a,b) for(int i=(a);i<(b);i++)
#define all(x) x.begin(),x.end()
#define fi first
#define se second
#define pb push_back
#define sp <<" "<<
#define cont(x) for(auto el:x) cout<<el<<' ';cout<<endl;
#define contp(x) for(auto el:x) cout<<el.fi<<'-'<<el.se<<' ';cout<<endl;
#define DEBUG(x) cout<<#x sp x<<endl;
#define carp(x,y) ((x%MOD)*(y%MOD))%MOD
#define topla(x,y) ((x%MOD)+(y%MOD))%MOD
#define mid (l+r)/2
const int MAXN=1e6+5;
const int MOD=1e9+7;
const int INF=1e18;
int n,m;
vi a;
vi adj[MAXN];
int d[MAXN], d2[MAXN];
int ans[MAXN];
pii tut[MAXN];
void dij(int bas){
set<pii> s;
s.insert({0,bas});
FORE(i,1,n+1) d[i]=INF;
d[bas]=0;
while(!s.empty()){
auto el=*s.begin();
s.erase(el);
int nd=el.se;
for(auto kom:adj[nd]){
int yeni=max(1+d[nd],a[kom]);
if(d[kom]>yeni){
if(d[kom]!=INF) s.erase({d[kom],kom});
d[kom]=yeni;
s.insert({d[kom],kom});
}
}
}
if(bas==1){
FORE(i,1,n+1) d2[i]=d[i];
}
}
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(0);
cin>>n>>m;
a.resize(n+1);
FORE(i,1,n+1) cin>>a[i];
FOR(i,m){
int u,v;
cin>>u>>v;
adj[u].pb(v);
adj[v].pb(u);
}
//varsay ki sürekli artırıyorum giderken
dij(1);
dij(n);
int res=INF;
FORE(i,1,n+1){
//hiç bekleme
res=min(res,max(d[i],d2[i])*2);
for(auto kom:adj[i]){
//1 kez bekle
res=min(res,max(d[i],d2[kom])*2+1);
res=min(res,max(d2[i],d[kom])*2+1);
}
}
cout<<res<<endl;
}
