import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int maxv = 0;
		boolean flg = true;
		for(int i = 0; i< N; i++) {
			int now = sc.nextInt();
			if(maxv < now) {
				maxv = now - 1;
			}else if(maxv == now){
				maxv = now;
			}else {
				flg = false;
				break;
			}
		}
		if(flg) {
			System.out.println("Yes");
		}else {
			System.out.println("No");
		}
	}

} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int maxv = 0;
		boolean flg = true;
		for(int i = 0; i< N; i++) {
			int now = sc.nextInt();
			if(maxv < now) {
				maxv = now - 1;
			}else if(maxv == now){
				maxv = now;
			}else {
				flg = false;
				break;
			}
		}
		if(flg) {
			System.out.println("Yes");
		}else {
			System.out.println("No");
		}
	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int maxv = 0;
		boolean flg = true;
		for(int i = 0; i< N; i++) {
			int now = sc.nextInt();
			if(maxv < now) {
				maxv = now - 1;
			}else if(maxv == now){
				maxv = now;
			}else {
				flg = false;
				break;
			}
		}
		if(flg) {
			System.out.println("Yes");
		}else {
			System.out.println("No");
		}
	} main {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int maxv = 0;
		boolean flg = true;
		for(int i = 0; i< N; i++) {
			int now = sc.nextInt();
			if(maxv < now) {
				maxv = now - 1;
			}else if(maxv == now){
				maxv = now;
			}else {
				flg = false;
				break;
			}
		}
		if(flg) {
			System.out.println("Yes");
		}else {
			System.out.println("No");
		}
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc int maxv = 0; maxv 0 boolean flg = true; flg true for(int i = 0; i< N; i++) {
			int now = sc.nextInt();
			if(maxv < now) {
				maxv = now - 1;
			}else if(maxv == now){
				maxv = now;
			}else {
				flg = false;
				break;
			}
		} int i = 0; int i = 0; i 0 i< N i N i++ i++ i {
			int now = sc.nextInt();
			if(maxv < now) {
				maxv = now - 1;
			}else if(maxv == now){
				maxv = now;
			}else {
				flg = false;
				break;
			}
		} {
			int now = sc.nextInt();
			if(maxv < now) {
				maxv = now - 1;
			}else if(maxv == now){
				maxv = now;
			}else {
				flg = false;
				break;
			}
		} int now = sc.nextInt(); now sc.nextInt() sc.nextInt sc if(maxv < now) {
				maxv = now - 1;
			}else if(maxv == now){
				maxv = now;
			}else {
				flg = false;
				break;
			} maxv < now maxv now {
				maxv = now - 1;
			} maxv = now - 1 maxv now - 1 now 1 if(maxv == now){
				maxv = now;
			}else {
				flg = false;
				break;
			} maxv == now maxv now {
				maxv = now;
			} maxv = now maxv now {
				flg = false;
				break;
			} flg = false flg false break; if(flg) {
			System.out.println("Yes");
		}else {
			System.out.println("No");
		} flg {
			System.out.println("Yes");
		} System.out.println("Yes") System.out.println System.out System System.out "Yes" {
			System.out.println("No");
		} System.out.println("No") System.out.println System.out System System.out "No" String[] args args public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int maxv = 0;
		boolean flg = true;
		for(int i = 0; i< N; i++) {
			int now = sc.nextInt();
			if(maxv < now) {
				maxv = now - 1;
			}else if(maxv == now){
				maxv = now;
			}else {
				flg = false;
				break;
			}
		}
		if(flg) {
			System.out.println("Yes");
		}else {
			System.out.println("No");
		}
	}

} public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int maxv = 0;
		boolean flg = true;
		for(int i = 0; i< N; i++) {
			int now = sc.nextInt();
			if(maxv < now) {
				maxv = now - 1;
			}else if(maxv == now){
				maxv = now;
			}else {
				flg = false;
				break;
			}
		}
		if(flg) {
			System.out.println("Yes");
		}else {
			System.out.println("No");
		}
	}

} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int maxv = 0;
		boolean flg = true;
		for(int i = 0; i< N; i++) {
			int now = sc.nextInt();
			if(maxv < now) {
				maxv = now - 1;
			}else if(maxv == now){
				maxv = now;
			}else {
				flg = false;
				break;
			}
		}
		if(flg) {
			System.out.println("Yes");
		}else {
			System.out.println("No");
		}
	}

}