#include <bits/stdc++.h>
using namespace std;
#define fileio() freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout)
#define fastio() cin.tie(0), ios_base::sync_with_stdio(0)
#define sp " "
#define endl "\n"
#define pii pair<int, int>
#define st first
#define nd second
#define pb push_back
#define N 300005
#define int long long
const int INF = 2e18 + 7;
int d[2][N];
vector<int> adj[N];
int arr[N];
int32_t main(){
//fileio();
fastio();
int n, m;
cin>>n>>m;
int maks = 0;
for (int i = 1; i <= n; i++){
cin>>arr[i];
maks = max(maks, arr[i]);
}
for (int i = 1; i <= m; i++){
int u, v;
cin>>u>>v;
adj[u].pb(v);
adj[v].pb(u);
}
d[0][1] = 0;
for (int i = 2; i <= n; i++){
d[0][i] = max(arr[i], d[0][i - 1] + 1);
}
d[1][n] = 0;
for (int i = n - 1; i >= 1; i--){
d[1][i] = max(arr[i], d[1][i + 1] + 1);
}
int ans = INF;
for (int i = 1; i <= n; i++){
if (arr[i] == maks) ans = min(ans, d[0][i] + d[1][i]);
}
cout<<ans<<endl;
cerr<<"time taken : "<<(float)clock() / CLOCKS_PER_SEC<<" seconds\n";
}
