#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define vi vector<long long>
#define all(x) x.begin(), x.end()
#define endl "\n"
#define pr pair<ll, ll>
#define ff first
#define ss second
void solution();
int main(){
ios::sync_with_stdio(false);
cin.tie(nullptr);
solution();
return 0;
}
#define arr array<ll, 4>
const int N = 2e5+10;
vi adj[N];
ll a[N];
void solution() {
ll n, m; cin >> n >> m;
for (int i = 1; i <= n; i++) cin >> a[i];
while (m--) {
int u, v; cin >> u >> v;
adj[u].push_back(v);
adj[v].push_back(u);
}
vi suf(n+2);
for (int i = n; i >= 1; i--) suf[i] = max(suf[i+1], a[i]);
ll x = 0;
ll ans = 0;
for (int i = 2; i < n; i++) {
if (suf[i] > x) {
if (a[i] > x) {
ll delta = a[i]-x;
x += delta;
ans+=delta;
} else ans++;
} else {
ans++;
if (suf[i] <= x-1) x--;
}
}
cout << ans + x << endl;
}
