/*
Author: Nguyen Chi Thanh - High School for the Gifted - VNU.HCM (i2528)
*/
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ull unsigned long long
#define ld long double
#define pii pair<int, int>
#define fi first
#define se second
#define __builtin_popcount __builtin_popcountll
#define all(x) (x).begin(), (x).end()
#define BIT(x, i) (((x) >> (i)) & 1)
#define MASK(x) ((1ll << (x)))
#define debug(a, l, r) for (int _i = (l); _i <= (r); ++_i) cout << (a)[_i] << ' '; cout << '\n';
const int MAXN = 2e5 + 5;
const int INF = 1e18 + 5;
int n, m, a[MAXN];
int dist1[MAXN], distn[MAXN];
vector<int> adj[MAXN];
void init() {
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].push_back(v);
adj[v].push_back(u);
}
}
void dijkstra(int source, int dist[]) {
for (int i = 1; i <= n; ++i) dist[i] = INF;
dist[source] = 0;
priority_queue<pii, vector<pii>, greater<pii>> pq;
pq.push({dist[source], source});
while (!pq.empty()) {
int cost = pq.top().fi, u = pq.top().se;
pq.pop();
if (dist[u] > cost) continue;
for (int v : adj[u]) {
int cost = max(dist[u] + 1, a[v]);
if (dist[v] > cost) {
dist[v] = cost;
pq.push({dist[v], v});
}
}
}
}
void solve() {
dijkstra(1, dist1);
dijkstra(n, distn);
int res = INF;
// Relax from all nodes
for (int i = 1; i <= n; ++i) {
int cost = max(dist1[i], distn[i]);
res = min(res, cost * 2);
}
// Relax from all edges
for (int u = 1; u <= n; ++u) {
for (int v : adj[u]) {
// if (a[u] < a[v]) continue;
// cout << u << ' ' << v << '\n';
int cost = 2 * max(dist1[u], distn[v]) + 1;
// cout << "Cost: " << cost << '\n';
res = min(res, cost);
}
}
// debug(dist1, 1, n);
// debug(distn, 1, n);
cout << res;
}
signed main() {
#ifdef NCTHANH
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
ios_base::sync_with_stdio(0);
cin.tie(nullptr); cout.tie(nullptr);
init();
solve();
return 0;
}
