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