#include "testlib.h"
#include <bits/stdc++.h>

using namespace std;
using pi=pair<int,int>;

int n,m;
vector<int> h;
vector<pi> xy;

void reverseProblem(){
  reverse(h.begin(),h.end());
  for(int i=0;i<m;i++){
    swap(xy[i].first,xy[i].second);
    xy[i].first=n-1-xy[i].first;
    xy[i].second=n-1-xy[i].second;
  }
}

long long solve(){
  vector<vector<long long>> dp(n,vector<long long>(2,-8e18));
  dp[0][0]=0;
  dp[0][1]=0;
  vector<vector<int>> g(n);
  for(int i=0;i<m;i++){
    g[xy[i].first].push_back(xy[i].second);
  }
  for(int i=0;i<n;i++){
    for(auto &nx : g[i]){
      if(h[i]<h[nx]){dp[nx][1]=max(dp[nx][1],dp[i][0]+h[nx]-h[i]);}
      else{dp[nx][0]=max(dp[nx][0],max(dp[i][0],dp[i][1]));}
    }
  }
  long long res=max(dp[n-1][0],dp[n-1][1]);
  if(res<0){res=-1;}
  return res;
}

int main(){
  registerValidation();
  n=inf.readInt(2,100000);inf.readSpace();
  m=inf.readInt(1,150000);inf.readEoln();
  h=inf.readInts(n,0,1000000000);inf.readEoln();
  xy.resize(m);
  set<pi> st;
  for(int i=0;i<m;i++){
    xy[i].first=inf.readInt(1,n);inf.readSpace();
    xy[i].second=inf.readInt(xy[i].first+1,n);inf.readEoln();
    xy[i].first--;xy[i].second--;
    st.insert(xy[i]);
    ensuref(h[xy[i].first]!=h[xy[i].second],"This is not a stairs");
  }
  ensuref(st.size()==m,"doubled stairs");
  inf.readEof();

  cout << solve() << "\n";
  reverseProblem();
  cout << solve() << "\n";
  return 0;
}