import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int[] h = new int[n];
		int i;
		for(i = 0; i < n; i++) {
			h[i] = scan.nextInt();
		}
		for(i = n - 1; i >= 1; i--) {
			if(h[i] >= h[i - 1]) {

			}else if(h[i - 1] - h[i] == 1) {
				h[i - 1]--;
			}else {
				System.out.println("No");
				return;
			}
		}
		System.out.println("Yes");
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int[] h = new int[n];
		int i;
		for(i = 0; i < n; i++) {
			h[i] = scan.nextInt();
		}
		for(i = n - 1; i >= 1; i--) {
			if(h[i] >= h[i - 1]) {

			}else if(h[i - 1] - h[i] == 1) {
				h[i - 1]--;
			}else {
				System.out.println("No");
				return;
			}
		}
		System.out.println("Yes");
	}
} Main public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int[] h = new int[n];
		int i;
		for(i = 0; i < n; i++) {
			h[i] = scan.nextInt();
		}
		for(i = n - 1; i >= 1; i--) {
			if(h[i] >= h[i - 1]) {

			}else if(h[i - 1] - h[i] == 1) {
				h[i - 1]--;
			}else {
				System.out.println("No");
				return;
			}
		}
		System.out.println("Yes");
	} main {
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int[] h = new int[n];
		int i;
		for(i = 0; i < n; i++) {
			h[i] = scan.nextInt();
		}
		for(i = n - 1; i >= 1; i--) {
			if(h[i] >= h[i - 1]) {

			}else if(h[i - 1] - h[i] == 1) {
				h[i - 1]--;
			}else {
				System.out.println("No");
				return;
			}
		}
		System.out.println("Yes");
	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int n = scan.nextInt(); n scan.nextInt() scan.nextInt scan int[] h = new int[n]; h new int[n] n int i; i for(i = 0; i < n; i++) {
			h[i] = scan.nextInt();
		} i = 0; i = 0 i 0 i < n i n i++ i++ i {
			h[i] = scan.nextInt();
		} {
			h[i] = scan.nextInt();
		} h[i] = scan.nextInt() h[i] h i scan.nextInt() scan.nextInt scan for(i = n - 1; i >= 1; i--) {
			if(h[i] >= h[i - 1]) {

			}else if(h[i - 1] - h[i] == 1) {
				h[i - 1]--;
			}else {
				System.out.println("No");
				return;
			}
		} i = n - 1; i = n - 1 i n - 1 n 1 i >= 1 i 1 i-- i-- i {
			if(h[i] >= h[i - 1]) {

			}else if(h[i - 1] - h[i] == 1) {
				h[i - 1]--;
			}else {
				System.out.println("No");
				return;
			}
		} {
			if(h[i] >= h[i - 1]) {

			}else if(h[i - 1] - h[i] == 1) {
				h[i - 1]--;
			}else {
				System.out.println("No");
				return;
			}
		} if(h[i] >= h[i - 1]) {

			}else if(h[i - 1] - h[i] == 1) {
				h[i - 1]--;
			}else {
				System.out.println("No");
				return;
			} h[i] >= h[i - 1] h[i] h i h[i - 1] h i - 1 i 1 {

			} if(h[i - 1] - h[i] == 1) {
				h[i - 1]--;
			}else {
				System.out.println("No");
				return;
			} h[i - 1] - h[i] == 1 h[i - 1] - h[i] h[i - 1] h i - 1 i 1 h[i] h i 1 {
				h[i - 1]--;
			} h[i - 1]-- h[i - 1] h i - 1 i 1 {
				System.out.println("No");
				return;
			} System.out.println("No") System.out.println System.out System System.out "No" return; System.out.println("Yes") System.out.println System.out System System.out "Yes" String[] args args public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int[] h = new int[n];
		int i;
		for(i = 0; i < n; i++) {
			h[i] = scan.nextInt();
		}
		for(i = n - 1; i >= 1; i--) {
			if(h[i] >= h[i - 1]) {

			}else if(h[i - 1] - h[i] == 1) {
				h[i - 1]--;
			}else {
				System.out.println("No");
				return;
			}
		}
		System.out.println("Yes");
	}
} public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int[] h = new int[n];
		int i;
		for(i = 0; i < n; i++) {
			h[i] = scan.nextInt();
		}
		for(i = n - 1; i >= 1; i--) {
			if(h[i] >= h[i - 1]) {

			}else if(h[i - 1] - h[i] == 1) {
				h[i - 1]--;
			}else {
				System.out.println("No");
				return;
			}
		}
		System.out.println("Yes");
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int[] h = new int[n];
		int i;
		for(i = 0; i < n; i++) {
			h[i] = scan.nextInt();
		}
		for(i = n - 1; i >= 1; i--) {
			if(h[i] >= h[i - 1]) {

			}else if(h[i - 1] - h[i] == 1) {
				h[i - 1]--;
			}else {
				System.out.println("No");
				return;
			}
		}
		System.out.println("Yes");
	}
}