/*
#pragma GCC optimize("Ofast,unroll-loops")
#pragma GCC target("avx2,fma,bmi,bmi2,sse4.2,popcnt,lzcnt")
*/
#include <bits/stdc++.h>
#define taskname ""
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define i64 long long
#define isz(x) (int)x.size()
using namespace std;
void solve() {
int n, m;
cin >> n >> m;
vector<int> a(n);
for (int i = 0; i < n; ++i) {
cin >> a[i];
}
vector<vector<int>> g(n);
for (int i = 0; i < m; ++i) {
int u, v;
cin >> u >> v;
--u, --v;
g[u].emplace_back(v);
g[v].emplace_back(u);
}
const int inf = 1e9;
vector<int> dis1(n, inf);
priority_queue<pair<int, int>, vector<pair<int, int>>, greater<pair<int, int>>> pq;
pq.emplace(0, 0); dis1[0] = 0;
while (not pq.empty()) {
auto [d, u] = pq.top();
pq.pop();
if (d != dis1[u]) continue;
for (auto v : g[u]) {
int nd = max(d + 1, a[v]);
if (nd < dis1[v]) {
dis1[v] = nd;
pq.emplace(nd, v);
}
}
}
vector<int> disn(n, inf);
pq.emplace(0, n - 1); disn[n - 1] = 0;
while (not pq.empty()) {
auto [d, u] = pq.top();
pq.pop();
if (d != disn[u]) continue;
for (auto v : g[u]) {
int nd = max(d + 1, a[v]);
if (nd < disn[v]) {
disn[v] = nd;
pq.emplace(nd, v);
}
}
}
int res = inf;
for (int i = 0; i < n; ++i) {
res = min(res, max(dis1[i], disn[i]) * 2);
for (auto u : g[i]) {
res = min(res, max(dis1[i], disn[u]) * 2 + 1);
}
}
cout << res << endl;
}
signed main() {
#ifndef CDuongg
if (fopen(taskname".inp", "r"))
assert(freopen(taskname".inp", "r", stdin)), assert(freopen(taskname".out", "w", stdout));
#else
freopen("bai3.inp", "r", stdin);
freopen("bai3.out", "w", stdout);
auto start = chrono::high_resolution_clock::now();
#endif
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int t = 1; //cin >> t;
while(t--) solve();
#ifdef CDuongg
auto end = chrono::high_resolution_clock::now();
cout << "\n"; for(int i = 1; i <= 100; ++i) cout << '=';
cout << "\nExecution time: " << chrono::duration_cast<chrono::milliseconds> (end - start).count() << "[ms]" << endl;
#endif
}
