#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
using namespace std;
using std::cout;
using std::cin;
using std::endl;
using ll=long long;
using ld=long double;
ll ILL=2167167167167167167;
const int INF=2100000000;
const ll mod=1e9+7;
#define rep(i,a) for (int i=0;i<a;i++)
#define all(p) p.begin(),p.end()
template<class T> using _pq = priority_queue<T, vector<T>, greater<T>>;
template<class T> ll LB(vector<T> &v,T a){return lower_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> ll UB(vector<T> &v,T a){return upper_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> bool chmin(T &a,const T &b){if(a>b){a=b;return 1;}else return 0;}
template<class T> bool chmax(T &a,const T &b){if(a<b){a=b;return 1;}else return 0;}
template<class T> void So(vector<T> &v) {sort(v.begin(),v.end());}
template<class T> void Sore(vector<T> &v) {sort(v.begin(),v.end(),[](T x,T y){return x>y;});}
void yneos(bool a){if(a) cout<<"Yes\n"; else cout<<"No\n";}
template<class T> void vec_out(vector<T> &p){for(int i=0;i<(int)(p.size());i++){if(i) cout<<" ";cout<<p[i];}cout<<"\n";}
template<class T> T min(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmin(ans,x);return ans;}
template<class T> T max(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmax(ans,x);return ans;}


void solve();
// oddloop
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	
	int t=1;
	//cin>>t;
	rep(i,t) solve();
}

void solve(){
	int N,M;
	cin>>N>>M;
	vector<ll> H(N);
	rep(i,N) cin>>H[i];
	vector<vector<int>> A(N),B(N);
	rep(i,M){
		int a,b;
		cin>>a>>b;
		a--,b--;
		A[a].push_back(b);
		B[N-1-b].push_back(N-1-a);
	}
	rep(roop,2){
		if(roop){
			swap(A,B);
			reverse(all(H));
		}
		vector<ll> dp1(N,-ILL),dp2(N,-ILL);
		dp1[0]=0;
		rep(i,N){
			for(auto x:A[i]){
				if(H[i]<H[x]){
					chmax(dp2[x],dp1[i]+H[x]-H[i]);
				}else{
					chmax(dp1[x],max(dp1[i],dp2[i]));
				}
			}
		}
		cout<<max(-1ll,max(dp1[N-1],dp2[N-1]))<<"\n";
	}
}