#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>

template <class T>
using MinHeap = std::priority_queue<T, std::vector<T>, std::greater<T>>;

using lint = long long;
constexpr lint INF = 1LL << 30;

void solve() {
    int n, m;
    std::cin >> n >> m;

    std::vector<lint> ots(n);
    for (auto& t : ots) std::cin >> t;

    std::vector<std::pair<int, lint>> ps(m);
    for (auto& p : ps) {
        std::cin >> p.first >> p.second;
        --p.first;
    }
    std::sort(ps.begin(), ps.end());

    lint ok = INF, ng = -1;
    while (ok - ng > 1) {
        lint c = (ok + ng) / 2;
        auto ts = ots;

        MinHeap<lint> que;
        lint sum = 0;
        int j = 0;
        for (int i = 0; i < n; ++i) {
            while (j < m && ps[j].first <= i) {
                lint w = ps[j].second + c * ps[j].first;
                sum += w;
                que.push(w);
                ++j;
            }

            while (!que.empty() && que.top() - c * i <= 0) {
                sum -= que.top();
                que.pop();
            }

            ts[i] -= sum - c * i * que.size();
        }

        while (!que.empty()) que.pop();
        sum = 0;
        j = m - 1;
        for (int i = n - 1; i >= 0; --i) {
            while (j >= 0 && ps[j].first > i) {
                lint w = ps[j].second - c * ps[j].first;
                sum += w;
                que.push(w);
                --j;
            }

            while (!que.empty() && que.top() + c * i < 0) {
                sum -= que.top();
                que.pop();
            }

            ts[i] -= sum + c * i * que.size();
        }

        if (std::any_of(ts.begin(), ts.end(), [](auto x) { return x <= 0; })) {
            ng = c;
        } else {
            ok = c;
        }
    }

    std::cout << (ok == INF ? -1 : ok) << std::endl;
}

int main() {
    std::cin.tie(nullptr);
    std::cout.tie(nullptr);
    std::ios::sync_with_stdio(false);

    solve();

    return 0;
}