#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define int long long
#define FOR(i, a, b) for (int i = (a); i <= (b); i++)
#define FORD(i, a, b) for (int i = (b); i >= (a); i --)
#define REP(i, a) for (int i = 0; i < (a); ++i)
#define REPD(i, a) for (int i = (a) - 1; i >= 0; --i)
#define MASK(i) (1LL << (i))
#define BIT(x, i) (((x) >> (i)) & 1)
constexpr ll LINF = (1ll << 60);
constexpr int INF = (1ll << 30);
constexpr int Mod = 1e9 + 7;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
/*
Phu Trong from Nguyen Tat Thanh High School for gifted student
*/
template <class X, class Y>
bool minimize(X &x, const Y &y){
X eps = 1e-9;
if (x > y + eps) {x = y; return 1;}
return 0;
}
template <class X, class Y>
bool maximize(X &x, const Y &y){
X eps = 1e-9;
if (x + eps < y) {x = y; return 1;}
return 0;
}
#define MAX_NODE 200005
#define MAX_EDGE 400005
int numNode, numEdge;
int label[MAX_NODE];
vector<int> G[MAX_NODE];
struct Edge{
int u, v, w;
Edge(){}
Edge(int _u, int _v, int _w): u(_u), v(_v), w(_w){}
int other(int x){
return (x ^ u ^ v);
}
} edge[MAX_EDGE];
void dijkstra(int u, int minDist[]){
priority_queue<pair<int, int>, vector<pair<int, int>>, greater<pair<int, int>>> q;
q.emplace(0, u);
memset(minDist, 0x3f, (numNode + 1) * sizeof(int));
minDist[u] = 0;
while(q.size()){
int du, u; tie(du, u) = q.top(); q.pop();
if (du > minDist[u]) continue;
for (int&i : G[u]){
int v = edge[i].other(u);
if(minimize(minDist[v], max(minDist[u] + 1, label[v]))){
q.emplace(minDist[v], v);
}
}
}
}
int minDist[MAX_NODE], rminDist[MAX_NODE];
void process(void){
cin >> numNode >> numEdge;
for (int i = 1; i <= numNode; ++i) cin >> label[i];
for (int i = 1; i <= numEdge; ++i){
cin >> edge[i].u >> edge[i].v;
G[edge[i].u].emplace_back(i);
G[edge[i].v].emplace_back(i);
}
dijkstra(1, minDist);
dijkstra(numNode, rminDist);
int ans = LINF;
for (int i = 1; i <= numNode; ++i){
int cost = max(minDist[i], rminDist[i]) * 2;
minimize(ans, cost);
}
for (int i = 1; i <= numEdge; ++i){
int u = edge[i].u, v = edge[i].v;
minimize(ans, max(minDist[u], rminDist[v]) * 2 + 1);
minimize(ans, max(minDist[v], rminDist[u]) * 2 + 1);
}
cout << ans;
}
signed main(){
#define name "Whisper"
cin.tie(nullptr) -> sync_with_stdio(false);
//freopen(name".inp", "r", stdin);
//freopen(name".out", "w", stdout);
process();
return (0 ^ 0);
}
