

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