#include <bits/stdc++.h>
#define int long long
#define pb push_back
#define fs first
#define sc second
using namespace std;
const int N = 2e5 + 5, INF = 1e18;
int n, m, a[N];
vector<int> adj[N];
vector<pair<int, int>> edg;
vector<int> dij(int s){
vector<int> d(n + 1, INF);
priority_queue<pair<int, int>, vector<pair<int, int>>, greater<pair<int, int>>> pq;
d[s] = 0;
pq.push({0, s});
while(pq.size()){
auto [cw, u] = pq.top(); pq.pop();
if(cw > d[u]) continue;
for(auto v:adj[u]){
int w = max(a[v], d[u] + 1);
if(d[v] > w) d[v] = w, pq.push({w, v});
}
}
return d;
}
signed main(){
cin >> n >> m;
for(int i = 1; i <= n; i++) cin >> a[i];
for(int i = 1; i <= m; i++){
int u, v;
cin >> u >> v;
adj[u].pb(v);
adj[v].pb(u);
edg.pb({u, v});
edg.pb({v, u});
}
vector<int> mn1 = dij(1), mn2 = dij(n);
int ans = INF;
for(int i = 0; i <= n; i++) ans = min(ans, 2 * max(mn1[i], mn2[i]));
cout << ans << endl;
}
