#include <bits/stdc++.h>
using namespace std;
const int maxN = 4e5 + 5;
const int INF = 1e9;
int N, M, a[maxN];
vector<int> adj[maxN];
pair<int, int> edge[maxN];
int f[maxN], g[maxN];
priority_queue<pair<int, int>, vector<pair<int, int>>, greater<pair<int, int>>> Q;
void dijsktra(int s, int d[]){
for(int i = 1; i <= N; ++i)d[i] = INF;
d[s] = 0;
Q.push({0, s});
while(!Q.empty()){
int dist = Q.top().first;
int u = Q.top().second;
Q.pop();
if(dist > d[u])continue;
for(int v : adj[u]){
int w = max(a[v], dist + 1);
if(w < d[v]){
d[v] = w;
Q.push({w, v});
}
}
}
}
int main(){
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
cin >> N >> M;
for(int i = 1; i <= N; ++i){
cin >> a[i];
}
for(int i = 1, u, v; i <= M; ++i){
cin >> u >> v ;
adj[u].push_back(v);
adj[v].push_back(u);
edge[i] = make_pair(u, v);
}
dijsktra(1, f);
dijsktra(N, g);
int res = INF;
for(int i = 1; i <= N; ++i){
res = min(res, f[i] + g[i] + abs(f[i] - g[i]));
}
for(int i = 1; i <= M; ++i){
int u = edge[i].first, v = edge[i].second;
if(f[u] == g[v])res = min(res, f[u] + g[v] + 1);
if(f[v] == g[u])res = min(res, f[v] + g[u] + 1);
}
cout << res;
return 0;
}
