#include <bits/stdc++.h>

using namespace std;

vector <long long> Aint;
vector <pair <int, int>> Interval;

void Update (int nod, int st, int dr, long long val, int poz)
{
	if (st == dr)
	{
		Aint[nod] += val;
		return;
	}
	int mij = st + dr >> 1;
	if (poz <= mij)
		Update(nod << 1, st, mij, val, poz);
	else Update(nod << 1 | 1, mij + 1, dr, val, poz);
	Aint[nod] = max (Aint[nod << 1], Aint[nod << 1 | 1]);
}
long long RangeQuerry (int nod, int st, int dr, int a, int b)
{
	if (a <= st && dr <= b)
		return Aint[nod];
	int mij = st + dr >> 1;
	long long MaxLeft = 0;
	long long MaxRight = 0;
	if (a <= mij)
		MaxLeft = RangeQuerry(nod << 1, st, mij, a, b);
	if (mij < b)
		MaxRight = RangeQuerry(nod << 1 | 1, mij + 1, dr, a, b);
	return max (MaxLeft, MaxRight);
}
int main(int argc, char const *argv[])
{
	ifstream fin ("chimic.in");
	ofstream fout ("chimic.out");
	int n;
	fin >> n;
	Aint.resize(n<<2);
	Interval.resize(n+1);
	fill(Aint.begin(), Aint.end(), 0);
	for (int i = 1; i <= n; ++i)
	{
		int x;
		fin >> x;
		Update (1, 1, n, 1LL*x, i);
	}
	for (int i = 1; i <= n; ++i)
		fin >> Interval[i].first >> Interval[i].second;
	for (int i = n; i >= 1; --i)
	{
		if (Interval[i].first == -1) continue;
		long long maxim = RangeQuerry(1, 1, n, Interval[i].first, Interval[i].second);
		Update(1, 1, n, maxim, i);
	}
	fout << Aint[1];
	return 0;
}