#include <bits/stdc++.h>
using namespace std;
#define MASK(x) (1LL << (x))
#define BIT(x, i) (((x) >> (i)) & 1)
#define ALL(x) (x).begin(), (x).end()
#define REP(i, n) for (int i = 0, _n = n; i < _n; ++i)
#define FOR(i, a, b) for (int i = (a), _b = (b); i <= _b; ++i)
#define FORD(i, a, b) for (int i = (a), _b = (b); i >= _b; --i)
#define FORE(i, a, b) for (int i = (a), _b = (b); i < _b; ++i)
#define debug(...) "[" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "] "
#define file(name) if (fopen(name".inp", "r")) { freopen(name".inp", "r", stdin); freopen(name".out", "w", stdout); }
template <class A, class B> bool minimize(A &a, B b) { if (a > b) { a = b; return true; } return false; }
template <class A, class B> bool maximize(A &a, B b) { if (a < b) { a = b; return true; } return false; }
const int MAXN = 2e5 + 5;
int N, M, a[MAXN], dpL[MAXN], dpR[MAXN];
vector <int> adj[MAXN];
void dijkstra(int s, int dp[]) {
fill(dp + 1, dp + N + 1, 1e9);
dp[s] = a[s];
priority_queue <pair <int, int>, vector <pair <int, int>>, greater_equal <pair <int, int>>> q;
q.emplace(dp[s], s);
while(q.size()) {
auto [du, u] = q.top(); q.pop();
if(dp[u] != du) continue;
for (auto v : adj[u]) if(minimize(dp[v], max(dp[u] + 1, a[v]))) {
q.emplace(dp[v], v);
}
}
}
void you_make_it(void) {
cin >> N >> M;
FOR(i, 1, N) cin >> a[i];
while(M--) {
int u, v; cin >> u >> v;
adj[u].emplace_back(v);
adj[v].emplace_back(u);
}
int res = 2e9;
dijkstra(1, dpL);
dijkstra(N, dpR);
FOR(i, 1, N) {
minimize(res, 2 * max(dpL[i], dpR[i]));
}
// FOR(i, 1, N) cout << dpL[i] << " \n"[i == N];
// FOR(i, 1, N) cout << dpR[i] << " \n"[i == N];
FOR(u, 1, N) for (auto v : adj[u]) {
minimize(res, 2 * max(dpL[u], dpR[v]) + 1);
}
cout << res;
}
signed main() {
#ifdef LOCAL
freopen("TASK.inp", "r", stdin);
freopen("TASK.out", "w", stdout);
#endif
file("airplane");
auto start_time = chrono::steady_clock::now();
cin.tie(0), cout.tie(0) -> sync_with_stdio(0);
you_make_it();
auto end_time = chrono::steady_clock::now();
cerr << "\nExecution time : " << chrono::duration_cast <chrono::milliseconds> (end_time - start_time).count() << "[ms]" << endl;
return (0 ^ 0);
}
// Dream it. Wish it. Do it.
