#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pii pair<ll, ll>
#define fi first
#define sec second
#define ld long double
const int MAXN = 1e5;
const ll INF = 4e18;
const int MOD = 998244353;
ll dp_L[MAXN + 5], dp_R[MAXN + 5];
ll A[MAXN + 5];
vector<ll> adj[MAXN + 5];
int main(){
ios_base::sync_with_stdio(0); cin.tie(0);
int tc = 1;
// cin >> tc;
for(;tc--;){
ll N, M; cin >> N >> M;
for(int i = 1; i <= N; i++){
cin >> A[i];
dp_L[i] = dp_R[i] = INF;
}
for(int i = 1; i <= M; i++){
ll u, v; cin >> u >> v;
adj[u].push_back(v), adj[v].push_back(u);
}
priority_queue<pii> pq;
pq.push({0, 1});
for(;!pq.empty();){
auto [val, idx] = pq.top(); pq.pop();
val = -val;
for(auto i : adj[idx]){
if(dp_L[i] > max(val + 1, A[i])){
dp_L[i] = max(val + 1, A[i]);
pq.push({-dp_L[i], i});
}
}
}
pq.push({0, N});
for(;!pq.empty();){
auto [val, idx] = pq.top(); pq.pop();
val = -val;
for(auto i : adj[idx]){
if(dp_R[i] > max(val + 1, A[i])){
dp_R[i] = max(val + 1, A[i]);
pq.push({-dp_R[i], i});
}
}
}
ll ans = INF;
for(int i = 1; i <= N; i++){
for(auto j : adj[i]){
ll MX = max(dp_L[i], dp_R[j]);
ans = min(ans, MX * 2 + 1);
}
ans = min(ans, max(dp_L[i], dp_R[i]) * 2);
}
cout << ans << "\n";
}
}
/*
*/
