#include<bits/stdc++.h>
using namespace std;
#define task "task"
#define ii pair<int,int>
#define fi first
#define se second
#define int long long
#define ll long long
#define ld double
#define mp make_pair
#define lg2 30
#define iii pair<int,ii>
#define iiii pair<ii,ii>
#define base 29
#define eps 1e-8
int dx[]= {0LL,0LL,1,-1,1,1,-1,-1};
int dy[]= {1,-1,0LL,0LL,1,-1,1,-1};
const int maxn=4e5+1;
const int mod=1e9+7;
int dist[2][maxn],n,m,w[maxn];
vector<int>a[maxn];
void dijk(int st,int dist[])
{
for(int i=1;i<=n;i++)dist[i]=1e18;
dist[st]=0;
priority_queue<ii,vector<ii>,greater<ii>>pq;
pq.push({0LL,st});
while(!pq.empty())
{
ii t=pq.top();
pq.pop();
if(t.fi!=dist[t.se])continue;
for(int v:a[t.se])
{
int val=max(t.fi+1,w[v]);
if(dist[v]>val)
{
dist[v]=val;
pq.push({dist[v],v});
}
}
}
}
void init()
{
cin>>n>>m;
for(int i=1;i<=n;i++)cin>>w[i];
for(int i=1;i<=m;i++)
{
int u,v;
cin>>u>>v;
a[u].push_back(v);
a[v].push_back(u);
}
dijk(1,dist[0]);
dijk(n,dist[1]);
int ans=1e18;
for(int i=1;i<=n;i++)
{
ans=min(ans,2*max(dist[0][i],dist[1][i]));
for(int v:a[i])
{
ans=min(ans,2*max(dist[0][i],dist[1][v])+1);
}
}
cout<<ans;
}
void process()
{
}
signed main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
if(fopen(task".inp","r"))
{
freopen(task".inp","r",stdin);
freopen(task".out","w",stdout);
}
init();
process();
cerr <<endl<< "TIME : " << clock() * 0.001 << "s" << endl ;
}
