#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, n) for (int i = 0; i < (n); i++)
#define repr(i, n) for (int i = (n) - 1; i >= 0; i--)
#define range(a) a.begin(), a.end()

int main() {
  ll N, M; cin >> N >> M;
  vector<ll> A(N); rep(i, N) cin >> A[i];
  vector<ll> X(M), W(M); rep(i, M) cin >> X[i] >> W[i], X[i]--;
  ll total = 0;
  rep(i, M) total += W[i];
  if (*min_element(range(A)) >= total) {
    cout << 0 << endl;
    return 0;
  }
  ll l = 0;
  ll r = 1e9;
  while (r - l > 1) {
    ll c = (l + r) / 2;
    vector<ll> sa(N + 1);
    vector<ll> sb(N + 1);
    auto linear = [&](ll l, ll r, ll a, ll b) {
      // ax + b
      sa[l] += a;
      sa[r] -= a;
      sb[l] += b;
      sb[r] -= b;
    };
    rep(j, M) {
      //    -w[j] / c <= di <= w[j]/c
      ll L = max(0LL, X[j] - W[j] / c);
      ll R = min(N - 1, X[j] + W[j] / c);
      // 左側では W[j] + (i - X[j]) * C
      // 右側では W[j] - (i - X[j]) * C
      linear(L, X[j], c, W[j] - X[j] * c);
      linear(X[j], R + 1, -c, W[j] + X[j] * c);
    }
    bool ok = true;
    rep(i, N) {
      sa[i + 1] += sa[i];
      sb[i + 1] += sb[i];
    }
    rep(i, N) {
      ok &= sa[i] * i + sb[i] <= A[i];
    }
    if (ok) r = c; else l = c;
  }
  if (r == 1e9) {
    cout << -1 << endl;
  } else {
    cout << r << endl;
  }
}