#include <iostream>
#include <fstream>
using namespace std;

int a[100000];

bool sift_down(int n, int i) {
	int MaxRoot = i;
	int l_child = 2 * i + 1;
	int r_child = 2 * i + 2;

	if (l_child < n && a[l_child] < a[MaxRoot])
		MaxRoot = l_child;

	if (r_child < n && a[r_child] < a[MaxRoot])
		MaxRoot = r_child;

	if (MaxRoot != i)
		return true;

	return false;
}

int main()
{
	ifstream fin("isheap.in");
	ofstream fout("isheap.out");
	int n;
	cin >> n;
	for (int i = 0; i < n; i++)
		cin >> a[i];

	for (int i = n / 2 - 1; i >= 0; i--) {
		if (sift_down(n, i)) {
			cout << "NO" << endl;
			return 0;
		}
	}
		cout << "YES" << endl;

	return 0;
}