#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll inf = 1e18;
int32_t main () {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int N, M;
cin >> N >> M;
vector<int> h(N), g[N];
vector<array<ll, 2>> dist(N);
for (int i = 0;i < N;i ++) {
cin >> h[i];
}
for (int i = 0;i < M;i ++) {
int u, v;
cin >> u >> v;
-- u;
-- v;
g[u].push_back(v);
g[v].push_back(u);
}
function<void(int, int)> dijikstra = [&](int si, int ti) -> void {
for (int i = 0;i < N;i ++) {
dist[i][ti] = inf;
}
dist[si][ti] = 0;
multiset<array<ll, 2>> dj;
dj.insert({dist[si][ti], si});
while (dj.size() > 0) {
auto [w, u] = *dj.begin();
dj.erase(dj.begin());
if (w != dist[u][ti]) continue;
for (auto v : g[u]) if (dist[v][ti] > max(1LL * h[v], dist[u][ti] + 1)) {
dist[v][ti] = max(1LL * h[v], dist[u][ti] + 1);
dj.insert({dist[v][ti], v});
}
}
};
dijikstra(0, 0);
dijikstra(N - 1, 1);
ll ans = inf;
for (int u = 0;u < N;u ++) {
ans = min(ans, max(dist[u][0], dist[u][1]) * 2);
for (auto v : g[u]) {
ans = min(ans, max(dist[v][0], dist[u][1]) * 2 + 1);
ans = min(ans, max(dist[u][0], dist[v][1]) * 2 + 1);
}
}
cout << ans << "\n";
}
