#include <iostream>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <tuple>
#include <cmath>
#include <numeric>
#include <functional>
#include <cassert>

#define debug_value(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << #x << "=" << x << endl;
#define debug(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << x << endl;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

using namespace std;
typedef long long ll;

int n, m;
ll a[100005];
int x[100005];
ll w[100005];

void input(){
    cin >> n >> m;
    for(int i = 0; i < n; i++){
        cin >> a[i];
    }
    for(int i = 0; i < m; i++){
        cin >> x[i] >> w[i];
        x[i]--;
    }
}

const ll INF = 1e18;

bool judge(ll c){
    if(c == 0){
        ll w_sum = 0;
        for(int i = 0; i < m; i++) w_sum += w[i];
        for(int i = 0; i < n; i++) {
            if(a[i] <= w_sum) return false;
        }
        return true;
    }
    vector<ll> d_load(n+5), load(n+5);
    auto add_d_load = [&](int l, int r, ll d){
        assert(l >= 0);
        // cout << l << ' ' << r << ' ' << d << endl;
        chmin(r, n);
        d_load[l] += d;
        d_load[r] -= d;
    };
    auto add_val = [&](int i, ll x){
        assert(i >= 0);
        assert(i < n);
        if(i == 0){
            load[0] += x;
            d_load[0] -= x;
            d_load[1] += x;
        }else{
            d_load[i-1] += x;
            d_load[i] -= 2*x;
            d_load[i+1] += x;
        }
    };
    for(int j = 0; j < m; j++){
        if(w[j] < c){
            // cout << 'H' << ' ' << x[j] << ' ' << w[j] << endl;
            add_val(x[j], w[j]);
            continue;
        }
        int l = x[j]-w[j]/c;
        if(l <= 0){
            // add_val(0, w[j]%c-c*l);
            load[0] += w[j]%c-c*l;
            l = 0;
        }else{
            add_d_load(l-1, l, w[j]%c);
        }
        add_d_load(x[j]+w[j]/c, x[j]+w[j]/c+1, -(w[j]%c));
        // cout << l << ' ' << w[j] << endl;
        add_d_load(l, x[j], c);
        add_d_load(x[j], x[j]+w[j]/c, -c);
    }
    for(int i = 0; i < n; i++) d_load[i+1] += d_load[i];
    for(int i = 0; i < n; i++) load[i+1] += load[i]+d_load[i];
    for(int i = 0; i < n; i++){
        // cout << load[i] << ' ' << a[i] << endl;
        if(load[i] >= a[i]) return false;
    }
    // debug_value(c);
    return true;
}

void solve(){
    if(judge(0)){
        cout << 0 << endl;
        return;
    }else if(!judge(INF)){
        cout << -1 << endl;
        return;
    }
    ll l = 0, r = INF;
    while(r-l > 1){
        ll c = (l+r)/2;
        // debug_value(c);
        if(judge(c)) r = c;
        else l = c;
    }
    cout << r << endl;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(10) << fixed;
    input();
    solve();
}