#include <bits/stdc++.h>
#define int long long
using namespace std;
int a,b;
int cnt[1000005];
int cnt1[1000005];
int bruh=1e16;
int height[1000005];
vector <int> z[1000005];
void dijkstra(){
for (int i=1;i<=a;i++){
cnt[i]=bruh;
}
priority_queue<pair<int,int>, vector<pair<int,int>> , greater<pair<int,int>> > q;
q.push({0,1});
cnt[1]=0;
while (q.size()){
pair<int,int> pos= q.top();
q.pop();
int val=pos.first;
int pos1=pos.second;
if (val>cnt[pos1]){
continue;
}
for (auto p:z[pos1]){
if (cnt[p]>max(height[p],cnt[pos1]+1)){
cnt[p]=max(height[p],cnt[pos1]+1);
q.push({cnt[p],p});
}
}
}
}
void dijkstra1(){
for (int i=1;i<=a;i++){
cnt1[i]=bruh;
}
priority_queue<pair<int,int>, vector<pair<int,int>> , greater<pair<int,int>> > q;
q.push({0,a});
cnt1[a]=0;
while (q.size()){
pair<int,int> pos= q.top();
q.pop();
int val=pos.first;
int pos1=pos.second;
if (val>cnt1[pos1]){
continue;
}
for (auto p:z[pos1]){
if (cnt1[p]>max(height[p],val+1)){
cnt1[p]=max(height[p],val+1);
q.push({cnt1[p],p});
}
}
}
}
signed main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin >> a >> b;
for (int i=1;i<=a;i++){
cin >> height[i];
}
for (int i=1;i<=b;i++){
int x,y;
cin >> x >> y;
z[x].push_back(y);
z[y].push_back(x);
}
dijkstra();
dijkstra1();
int min1=1e18;
for (int i=1;i<=a;i++){
min1=min(min1,2*max(cnt[i],cnt1[i]));
for (auto p:z[i]){
min1=min(min1,2*max(cnt[i],cnt1[p])+1);
}
}
cout << min1 << "\n";
return 0;
}
