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



int N;
int A[200010];

signed main() {
	cin >> N;
	for (int i = 0; i < N; i++)cin >> A[i];
	for (int i = 0; i < N; i++) {
		if (A[i] > i + 1) {
			cout << "No" << endl; return 0;
		}
	}
	vector<int>sum(N + 1);
	for (int i = 0; i < N; i++) {
		if (A[i] == i + 1) {
			A[i] = 0;
			sum[0]++; sum[i]--;
		}
	}
	for (int i = 1; i <= N; i++) {
		sum[i] += sum[i - 1];
	}
	for (int i = 0; i < N; i++) {
		A[i] += sum[i];
	}
	int idx = 0;
	for (int i = N - 1; i >= 0; i--) {
		if (A[i] != 0) {
			idx = i + 1; break;
		}
	}
	for (int i = 0; i < idx; i++) {
		if (A[i] != i + 1) {
			cout << "No" << endl; return 0;
		}
	}
	cout << "Yes" << endl;
	return 0;
}