#include<bits/stdc++.h>
#define ll long long
#define alls(x) x.begin(),x.end()
#define ull unsigned long long
#define lowbit(x) x&-x
#define lc p<<1
#define rc p<<1|1
#define PII pair<int,int>
#define vi vector<int>
// #define int long long

using namespace std;
const ll inf = 2e18;
const int mod = 998244353;
const int N = 2e5+10;
struct node{
    int x;
    int id;
};
void solve()
{
    int n,m;
    cin >> n >> m;
    vi a(n+1),b(n+1);
    for(int i = 1;i<=n;i++)
    {
        cin >> a[i];
        b[i] = a[i];
    }
    vector<queue<int>>q(n+1);
    vector<node>info(m+1);
    for(int i = 1;i<=m;i++)
    {
        cin >> info[i].x >> info[i].id;
        q[info[i].id].push(info[i].x);
    }
    priority_queue<PII,vector<PII>,greater<PII>>pq;//充电站位置，编号
    for(int i = 1;i<=n;i++)
    {
        if(q[i].size())
        {
            pq.push({q[i].front(),i});
            q[i].pop();
        }
        else
        {
            pq.push({2e9,i});
        }
    }
    bool f = true;
    ll ans = 0;//现在的位置
    for(int i = 1;i<=m;i++){
        int dis = info[i].x - ans;
        while (!pq.empty())
        {
            if(b[pq.top().second]>dis)
            {
                dis = 0;
                b[pq.top().second]-=dis;
            }
            else
            {
                dis -= b[pq.top().second];
                b[pq.top().second] = 0;
                pq.pop();
                break;
            }
        }
        if(dis)
        {
            f = false;
            ans += info[i].x - ans - dis;
            break;
        }
        if(!pq.empty() && pq.top().second==info[i].id)pq.pop();
        if(q[info[i].id].size())
        {
            pq.push({q[info[i].id].front(),info[i].id});
            q[info[i].id].pop();
        }
        else
        {
            pq.push({2e9,info[i].id});
        }
        b[info[i].id] = a[info[i].id];
        ans = info[i].x;
    }
    if(f){
        while(pq.size())
        {
            ans += b[pq.top().second];
        }
    }
    cout<<ans<<'\n';
}
signed main()
{
    cout<<fixed<<setprecision(6);
    ios::sync_with_stdio(false),cin.tie(nullptr),cout.tie(nullptr);
    int _ = 1;
    // cin >> _;
    while(_--)solve();
}