#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for(int i = 0; i < (int)(n); ++i)
#define all(x) x.begin(),x.end()
#define ln '\n'
const long long MOD = 1000000007LL;
//const long long MOD = 998244353LL;
typedef long long ll;
typedef unsigned long long ull; 
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;
template<class T> inline bool chmax(T &a, T b) { if (a < b) { a = b; return true;} return false; }
template<class T> inline bool chmin(T &a, T b) { if (a > b) { a = b; return true;} return false; }
///////////////////////////////////////////////////////////////////////////////////////////////////


template<typename T, typename U, typename F, typename G, typename H>
struct LazySegmentTree {
    T unitynode;
    U unitylazy;
    F f;
    G g;
    H h;
    int N;
    int height;
    vector<T> node;
    vector<U> lazy;

    LazySegmentTree(F f, G g, H h, T unitynode, U unitylazy) : f(f), g(g), h(h), unitynode(unitynode), unitylazy(unitylazy) {}

    void init(int sz) {
        N = 1;
        height = 0;
        while (N < sz) {
            N *= 2;
            ++height;
        }
        node.assign(2*N,unitynode);
        lazy.assign(2*N,unitylazy);
    }

    void set(int k, const T &val) {node[k+N] = val;}

    void build() {
        for (int i = N-1; i > 0; --i) {
            node[i] = f(node[i<<1|0],node[i<<1|1]);
        }
    }

    inline T reflect(int k) {
        return lazy[k] == unitylazy ? node[k] : g(node[k],lazy[k]);
    }

    void eval(int k) {
        if (lazy[k] == unitylazy) return;
        if (k < N) {
            lazy[k<<1|0] = h(lazy[k<<1|0],lazy[k]);
            lazy[k<<1|1] = h(lazy[k<<1|1],lazy[k]);
        }
        node[k] = reflect(k);
        lazy[k] = unitylazy;
    }

    inline void recalc(int k) {
        while (k >>= 1) {
            node[k] = f(reflect(k<<1|0),reflect(k<<1|1));
        }
    }

    // [l,r) (0-indexed)
    void update(int l, int r, U val) {
        if (l >= r) return;
        l += N; r += N-1;
        for (int i = height; i > 0; --i) {
            eval(l>>i);
            eval(r>>i);
        }
        int a = l; int b = r++;
        while (l < r) {
            if (l & 1) lazy[l] = h(lazy[l],val), ++l;
            if (r & 1) --r, lazy[r] = h(lazy[r],val);
            l >>= 1; r >>= 1;
        }
        recalc(a);
        recalc(b);
    }

    T get(int l, int r) {
        if (l >= r) return unitynode;
        l += N; r += N-1;
        for (int i = height; i > 0; --i) {
            eval(l>>i);
            eval(r>>i);
        }
        ++r;
        T vl = unitynode, vr = unitynode;
        while (l < r) {
            if (l & 1) vl = f(vl,reflect(l++));
            if (r & 1) vr = f(reflect(--r),vr);
            l >>= 1; r >>= 1;
        }
        return f(vl,vr);
    }

    T operator[](int x) {return reflect(x+N);}
};

using Tu = tuple<ll, ll,int>;

int main() {
    ios::sync_with_stdio(false); cin.tie(nullptr);
    int N,M; cin >> N >> M;
    vector<ll> A(N);
    vector<pll> X(M);
    rep(i,N) cin >> A[i];
    rep(i,M) {
        cin >> X[i].first >> X[i].second;
        --X[i].first;
    }

    sort(all(X));
    auto f=[](pll a, pll b) {
        if (a.first==0&&a.second==0) return b;
        if (b.first==0&&b.second==0) return a;
        ll p = a.first+b.first;
        ll q = max(a.second+b.first,b.second);
        return make_pair(p,q);
    };
    auto g=[](pll a, ll val) {
        a.first += val;
        return a;
    };
    auto h=[](ll a, ll b){
        return a+b;
    };
    const pll id1 = make_pair(0,0);
    const ll id2 = 0;
    LazySegmentTree<pll, ll, decltype(f), decltype(g), decltype(h)> seg(f,g,h,id1,id2);
    seg.init(M);
    rep(i,M) {
        seg.set(i,make_pair(X[i].second,0));
    }
    seg.build();
    ll ng = -1;
    ll ok = 1e5;
    while (ok - ng > 1) {
        ll mid = (ng+ok)/2;
        bool flag = true;
        rep(i,N) {
            if (i) {
                int k = lower_bound(all(X),make_pair(ll(i),-1LL)) - X.begin();
                seg.update(0,k,-mid);
                seg.update(k,M,+mid);
            }
            ll a,b;
            //cout << a << " " << b << ln;
            tie(a,b) = seg.get(0,M);
            //cout << a << " " << b << ln;
            if (A[i] <= max(a,b)) flag = false;
        }

        if (flag) ok = mid;
        else ng = mid;
    }
    if (ok==1e5) cout << -1 << ln;
    else cout << ok << ln;
}