import java.awt.*;
import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.math.BigInteger;
import java.util.*;

public class Main {
    public static void main(String[] args)throws IOException {
        Scanner sc = new Scanner(System.in);
        int n=sc.nextInt();
        int[] a=new int[n];
        for(int i=0;i<n;i++)a[i]=sc.nextInt();

        for(int i=0;i<n-1;i++){
            if(a[i]<a[i+1])a[i+1]--;
            else if(a[i]==a[i+1]);
            else {
                System.out.println("No");
                System.exit(0);
            }
        }
        System.out.println("Yes");
    }
} import java.awt.*; awt.* java import java.io.DataInputStream; DataInputStream java.io import java.io.FileInputStream; FileInputStream java.io import java.io.IOException; IOException java.io import java.math.BigInteger; BigInteger java.math import java.util.*; util.* java public class Main {
    public static void main(String[] args)throws IOException {
        Scanner sc = new Scanner(System.in);
        int n=sc.nextInt();
        int[] a=new int[n];
        for(int i=0;i<n;i++)a[i]=sc.nextInt();

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

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

        for(int i=0;i<n-1;i++){
            if(a[i]<a[i+1])a[i+1]--;
            else if(a[i]==a[i+1]);
            else {
                System.out.println("No");
                System.exit(0);
            }
        }
        System.out.println("Yes");
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n=sc.nextInt(); n sc.nextInt() sc.nextInt sc int[] a=new int[n]; a new int[n] n for(int i=0;i<n;i++)a[i]=sc.nextInt(); int i=0; int i=0; i 0 i<n i n i++ i++ i a[i]=sc.nextInt(); a[i]=sc.nextInt() a[i] a i sc.nextInt() sc.nextInt sc for(int i=0;i<n-1;i++){
            if(a[i]<a[i+1])a[i+1]--;
            else if(a[i]==a[i+1]);
            else {
                System.out.println("No");
                System.exit(0);
            }
        } int i=0; int i=0; i 0 i<n-1 i n-1 n 1 i++ i++ i {
            if(a[i]<a[i+1])a[i+1]--;
            else if(a[i]==a[i+1]);
            else {
                System.out.println("No");
                System.exit(0);
            }
        } {
            if(a[i]<a[i+1])a[i+1]--;
            else if(a[i]==a[i+1]);
            else {
                System.out.println("No");
                System.exit(0);
            }
        } if(a[i]<a[i+1])a[i+1]--;
            else if(a[i]==a[i+1]);
            else {
                System.out.println("No");
                System.exit(0);
            } a[i]<a[i+1] a[i] a i a[i+1] a i+1 i 1 a[i+1]-- a[i+1] a i+1 i 1 if(a[i]==a[i+1]);
            else {
                System.out.println("No");
                System.exit(0);
            } a[i]==a[i+1] a[i] a i a[i+1] a 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)throws IOException {
        Scanner sc = new Scanner(System.in);
        int n=sc.nextInt();
        int[] a=new int[n];
        for(int i=0;i<n;i++)a[i]=sc.nextInt();

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

        for(int i=0;i<n-1;i++){
            if(a[i]<a[i+1])a[i+1]--;
            else if(a[i]==a[i+1]);
            else {
                System.out.println("No");
                System.exit(0);
            }
        }
        System.out.println("Yes");
    }
} Main
import java.awt.*;
import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.math.BigInteger;
import java.util.*;

public class Main {
    public static void main(String[] args)throws IOException {
        Scanner sc = new Scanner(System.in);
        int n=sc.nextInt();
        int[] a=new int[n];
        for(int i=0;i<n;i++)a[i]=sc.nextInt();

        for(int i=0;i<n-1;i++){
            if(a[i]<a[i+1])a[i+1]--;
            else if(a[i]==a[i+1]);
            else {
                System.out.println("No");
                System.exit(0);
            }
        }
        System.out.println("Yes");
    }
}