import java.util.*;
public class Main{
	public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
      int n = sc.nextInt();
      int[] h = new int[n];
      for(int i = 0;i < n;i++){
      	h[i] = sc.nextInt();
      }
      boolean a = true;
      for(int i = n-2;i >= 0;i--){
      	if(h[i] > h[i+1])h[i]--;
      }
      for(int i = 0;i < n-1;i++){
      	if(h[i] <= h[i+1]) a &= true;
        else a = false;
      }
      if(a)System.out.println("Yes");
      else System.out.println("No");
    }
} import java.util.*; util.* java public class Main{
	public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
      int n = sc.nextInt();
      int[] h = new int[n];
      for(int i = 0;i < n;i++){
      	h[i] = sc.nextInt();
      }
      boolean a = true;
      for(int i = n-2;i >= 0;i--){
      	if(h[i] > h[i+1])h[i]--;
      }
      for(int i = 0;i < n-1;i++){
      	if(h[i] <= h[i+1]) a &= true;
        else a = false;
      }
      if(a)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[] h = new int[n];
      for(int i = 0;i < n;i++){
      	h[i] = sc.nextInt();
      }
      boolean a = true;
      for(int i = n-2;i >= 0;i--){
      	if(h[i] > h[i+1])h[i]--;
      }
      for(int i = 0;i < n-1;i++){
      	if(h[i] <= h[i+1]) a &= true;
        else a = false;
      }
      if(a)System.out.println("Yes");
      else System.out.println("No");
    } main {
    	Scanner sc = new Scanner(System.in);
      int n = sc.nextInt();
      int[] h = new int[n];
      for(int i = 0;i < n;i++){
      	h[i] = sc.nextInt();
      }
      boolean a = true;
      for(int i = n-2;i >= 0;i--){
      	if(h[i] > h[i+1])h[i]--;
      }
      for(int i = 0;i < n-1;i++){
      	if(h[i] <= h[i+1]) a &= true;
        else a = false;
      }
      if(a)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[] h = new int[n]; h new int[n] n for(int i = 0;i < n;i++){
      	h[i] = sc.nextInt();
      } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
      	h[i] = sc.nextInt();
      } {
      	h[i] = sc.nextInt();
      } h[i] = sc.nextInt() h[i] h i sc.nextInt() sc.nextInt sc boolean a = true; a true for(int i = n-2;i >= 0;i--){
      	if(h[i] > h[i+1])h[i]--;
      } int i = n-2; int i = n-2; i n-2 n 2 i >= 0 i 0 i-- i-- i {
      	if(h[i] > h[i+1])h[i]--;
      } {
      	if(h[i] > h[i+1])h[i]--;
      } if(h[i] > h[i+1])h[i]--; h[i] > h[i+1] h[i] h i h[i+1] h i+1 i 1 h[i]-- h[i] h i for(int i = 0;i < n-1;i++){
      	if(h[i] <= h[i+1]) a &= true;
        else a = false;
      } int i = 0; int i = 0; i 0 i < n-1 i n-1 n 1 i++ i++ i {
      	if(h[i] <= h[i+1]) a &= true;
        else a = false;
      } {
      	if(h[i] <= h[i+1]) a &= true;
        else a = false;
      } if(h[i] <= h[i+1]) a &= true;
        else a = false; h[i] <= h[i+1] h[i] h i h[i+1] h i+1 i 1 a &= true a true a = false a false if(a)System.out.println("Yes");
      else System.out.println("No"); a System.out.println("Yes") System.out.println System.out System System.out "Yes" 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[] h = new int[n];
      for(int i = 0;i < n;i++){
      	h[i] = sc.nextInt();
      }
      boolean a = true;
      for(int i = n-2;i >= 0;i--){
      	if(h[i] > h[i+1])h[i]--;
      }
      for(int i = 0;i < n-1;i++){
      	if(h[i] <= h[i+1]) a &= true;
        else a = false;
      }
      if(a)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[] h = new int[n];
      for(int i = 0;i < n;i++){
      	h[i] = sc.nextInt();
      }
      boolean a = true;
      for(int i = n-2;i >= 0;i--){
      	if(h[i] > h[i+1])h[i]--;
      }
      for(int i = 0;i < n-1;i++){
      	if(h[i] <= h[i+1]) a &= true;
        else a = false;
      }
      if(a)System.out.println("Yes");
      else System.out.println("No");
    }
} Main
import java.util.*;
public class Main{
	public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
      int n = sc.nextInt();
      int[] h = new int[n];
      for(int i = 0;i < n;i++){
      	h[i] = sc.nextInt();
      }
      boolean a = true;
      for(int i = n-2;i >= 0;i--){
      	if(h[i] > h[i+1])h[i]--;
      }
      for(int i = 0;i < n-1;i++){
      	if(h[i] <= h[i+1]) a &= true;
        else a = false;
      }
      if(a)System.out.println("Yes");
      else System.out.println("No");
    }
}
