#define _GLIBCXX_DEBUG
#include <iostream>
#include <vector>
#include <bitset>
#include <functional>
#include <queue>
#include <algorithm>
#include <map>
#include <set>
#include <cmath>
#include <tuple>
#include <cassert>
#include <string>
using namespace std;

template <class T> void chmax(T &x, T y) {if(x<y) x=y;}
template <class T> void chmin(T &x, T y) {if(x>y) x=y;}



main()
{
    ios::sync_with_stdio(false), cin.tie(nullptr);

    int n,m; cin>>n>>m;
    vector<int> a(n);
    for(int &e:a) cin>>e;
    vector<pair<int,int>> h(m);
    for(auto &e:h)
    {
        int x,w; cin>>x>>w; --x;
        e={x,w};
    }

    // binary search
    long long ok=1e5+1;
    long long ng=0;
    while(ok-ng>1)
    {
        long long c=(ok+ng)/2;
        vector<long long> b(n+1);
        for(auto &e:h)
        {
            int x,w; tie(x,w)=e;
            const int l=max(0LL,x-w/c);
            const int r=x+w/c+1;
            b[l+1]+=c;
            b[x+1]-=c*2;
            if(r<=n) b[r]+=c;
        }
        for(int i=0;i<n;++i)
        {
            b[i+1]+=b[i];
        }
        for(auto &e:h)
        {
            int x,w; tie(x,w)=e;
            const int l=max(0LL,x-w/c);
            const int r=x+w/c+1;
            b[l]+=w-c*(x-l);
            if(r<=n) b[r]-=w%c;
        }
        for(int i=0;i<n;++i)
        {
            b[i+1]+=b[i];
        }
        bool fail=0;
        for(int i=0;i<n;++i)
        {
            if(b[i]>a[i])
            {
                fail=1;
            }
        }
        if(fail)
        {
            ng=c;
        }
        else
        {
            ok=c;
        }
    }
    if(ng)
    {
        if(ok>1e5) cout << -1 << "\n";
        else cout << ok << "\n";
    }
    else
    {
        long long ws=0;
        for(auto &e:h)
        {
            ws+=e.second;
        }
        if(ws>*min_element(begin(a),end(a)))
        {
            cout << 1 << "\n";
        }
        else
        {
            cout << 0 << "\n";
        }
    }
}