#include<bits/stdc++.h>
using namespace std;
#define IOS cin.tie(nullptr)->sync_with_stdio(0),cin.exceptions(cin.failbit);
#define lb(x) (x)&-(x)
#define all(x) (x).begin(),(x).end()
#define ll long long
constexpr int maxN=2e5+5;
int n,m,h[maxN],dis[2][maxN];
vector<int> adj[maxN];
priority_queue<pair<int,int>,vector<pair<int,int>>,greater<pair<int,int>>> pq;
inline void dijkstra(int idx,int s){
fill(dis[idx],dis[idx]+n+1,1e9);
pq.emplace(dis[idx][s]=0,s);
for(;!pq.empty();){
auto [d,u] = pq.top();
pq.pop();
if(d!=dis[idx][u])continue;
for(int v:adj[u])if(dis[idx][v]>max(h[v],d+1))pq.emplace(dis[idx][v]=max(h[v],d+1),v);
}
}
int main(){
IOS
cin>>n>>m;
for(int i = 1;i<=n;i++)cin>>h[i];
for(int a,b;m--;)cin>>a>>b,adj[adj[a].emplace_back(b)].emplace_back(a);
dijkstra(0,1);
dijkstra(1,n);
int ans = 1e9;
for(int i = 1;i<=n;i++){
ans = min(ans,2*max(dis[0][i],dis[1][i]));
for(int v:adj[i])ans = min(ans,2*max(dis[0][i],dis[1][v])+1);
}
cout<<ans<<'\n';
}
