#include <bits/stdc++.h>
using namespace std;
main() {
cin.tie(0)->sync_with_stdio(0);
int n, m; cin >> n >> m;
if (n == 1) cout << "0\n", exit(0);
vector<int> h(n);
for (int &x : h) cin >> x;
vector<vector<int>> adj(n);
for (int i = 0; i < m; i++) {
int u, v; cin >> u >> v; u--, v--;
adj[u].push_back(v);
adj[v].push_back(u);
}
using t3 = tuple<int, int, int>;
auto funny_dijkstra = [&] (int s, vector<int> &dist, vector<int> &alt) {
priority_queue<t3, vector<t3>, greater<>> pq;
pq.push({h[s], h[s], s});
while (pq.size()) {
auto [d, a, u] = pq.top(); pq.pop();
if (dist[u] < d) continue;
dist[u] = d, alt[u] = a;
for (int v : adj[u]) {
int ndist = max(d + 1, h[v]);
if (ndist < dist[v])
pq.push({ndist, max(alt[u], h[v]), v});
}
}
};
vector<int> dist0(n, 1e9), dist1(n, 1e9), alt0(n), alt1(n);
funny_dijkstra(0, dist0, alt0);
funny_dijkstra(n - 1, dist1, alt1);
int ans = 1e9;
for (int i = 0; i < n; i++) {
if (alt0[i] == alt1[i])
ans = min(ans, dist0[i] + dist1[i]);
}
cout << ans << '\n';
}
