#include <bits/stdc++.h>
using namespace std;

void fast_io() {
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
}

int main() {
	fast_io();
	int n;
	cin >> n;
	vector<int> a(n);
	for (int i = 0; i < n; i++) {
		cin >> a[i];
	}
	for (int i = 0; i < n - 1; i++) {
		if (abs(a[i] - a[i + 1]) > 1) {
			cout << "No" << endl;
			return 0;
		}
	}
	cout << "Yes" << endl;
}