#include <bits/stdc++.h>
using namespace std;
const long long mod = (long long)1e9 + 7;
const long long inf = (long long)1e16;
const long double eps = 1e-12;
const long long N = (int)2e5 + 5;
const long long LOGN = 19;
const long double PI = 3.14159265358979323846;
inline long long mul(long long a, long long b, long long m = mod) {
  return (long long)(a * b) % m;
}
inline long long add(long long a, long long b, long long m = mod) {
  a += b;
  if (a >= m) a -= m;
  if (a < 0) a += m;
  return a;
}
inline long long power(long long a, long long b, long long m = mod) {
  if (b == 0) return 1;
  if (b == 1) return (a % m);
  long long x = power(a, b / 2, m);
  x = mul(x, x, m);
  if (b % 2) x = mul(x, a, m);
  return x;
}
int n, m;
int k[N], rem[N];
bool ok[N];
vector<int> d[N], temp[(int)5e5 + 5];
vector<int> tmp[(int)5e5 + 5];
bool check(int mid) {
  for (int i = 1; i <= n; i++) {
    ok[i] = false;
    rem[i] = k[i];
  }
  for (int i = 1; i <= mid; i++) temp[i].clear(), tmp[i].clear();
  for (int i = 1; i <= n; i++) {
    int last = -1;
    for (int u : d[i]) {
      if (u > mid) continue;
      last = max(last, u);
    }
    if (last != -1) temp[last].push_back(i);
  }
  int taken = 0, left = 0;
  for (int i = 1; i <= mid; i++) {
    left++;
    for (int chk : temp[i]) {
      if (rem[chk] > 0) {
        int take = min(rem[chk], left);
        taken += take;
        rem[chk] -= take;
        left -= take;
      }
      if (left == 0) break;
    }
  }
  int go = 0;
  for (int i = 1; i <= n; i++) go += rem[i];
  return (2 * go <= left);
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  if (0) {
    freopen("C:\\Users\\Dishant\\Desktop\\Collection-DEV c++\\input.txt", "r",
            stdin);
    freopen("C:\\Users\\Dishant\\Desktop\\Collection-DEV c++\\output.txt", "w",
            stdout);
  }
  cin >> n >> m;
  for (int i = 1; i <= n; i++) cin >> k[i];
  for (int i = 0; i < m; i++) {
    int t, tt;
    cin >> t >> tt;
    d[tt].push_back(t);
  }
  int ans = -1;
  int low = 1, high = (int)5e5;
  while (low <= high) {
    int mid = (low + high) >> 1;
    if (check(mid)) {
      high = mid - 1;
      ans = mid;
    } else
      low = mid + 1;
  }
  cout << ans;
  return 0;
}
