// GPT
#include "bits/stdc++.h"
using namespace std;
using ll = long long;
static const ll INF = (1LL << 62);
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n, m;
cin >> n >> m;
vector<ll> a(n + 1);
for (int i = 1; i <= n; ++i) cin >> a[i];
vector<vector<int>> adj(n + 1);
vector<pair<int,int>> edges;
edges.reserve(m);
for (int i = 0; i < m; ++i) {
int u, v;
cin >> u >> v;
adj[u].push_back(v);
adj[v].push_back(u);
edges.push_back({u, v});
}
auto dijkstra = [&](int src) {
vector<ll> dist(n + 1, INF);
priority_queue<pair<ll,int>, vector<pair<ll,int>>, greater<pair<ll,int>>> pq;
dist[src] = 0;
pq.push({0, src});
while (!pq.empty()) {
auto [d, u] = pq.top();
pq.pop();
if (d != dist[u]) continue;
for (int v : adj[u]) {
ll nd = max(d + 1, a[v]);
if (nd < dist[v]) {
dist[v] = nd;
pq.push({nd, v});
}
}
}
return dist;
};
vector<ll> d1 = dijkstra(1);
vector<ll> d2 = dijkstra(n);
ll ans = INF;
for (int i = 1; i <= n; ++i) {
ans = min(ans, 2 * max(d1[i], d2[i]));
}
for (auto [u, v] : edges) {
ans = min(ans, 2 * max(d1[u], d2[v]) + 1);
ans = min(ans, 2 * max(d1[v], d2[u]) + 1);
}
cout << ans << '\n';
return 0;
}
