import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		int n =sc.nextInt();
		int[] h = new int[100000001];
		boolean flag=false;
		for(int i=0;i<n;i++) {
			h[i]=sc.nextInt();
			if( i!=0 && h[i]>h[i-1] ) {
					h[i]--;
			}
		}
		for(int i=0;i<n;i++) {
			if(i!=0 && h[i]<h[i-1]) {
				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 sc = new Scanner(System.in);
		int n =sc.nextInt();
		int[] h = new int[100000001];
		boolean flag=false;
		for(int i=0;i<n;i++) {
			h[i]=sc.nextInt();
			if( i!=0 && h[i]>h[i-1] ) {
					h[i]--;
			}
		}
		for(int i=0;i<n;i++) {
			if(i!=0 && h[i]<h[i-1]) {
				System.out.println("No");
				return;
			}
		}
		System.out.println("Yes");
	}
} Main public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		int n =sc.nextInt();
		int[] h = new int[100000001];
		boolean flag=false;
		for(int i=0;i<n;i++) {
			h[i]=sc.nextInt();
			if( i!=0 && h[i]>h[i-1] ) {
					h[i]--;
			}
		}
		for(int i=0;i<n;i++) {
			if(i!=0 && h[i]<h[i-1]) {
				System.out.println("No");
				return;
			}
		}
		System.out.println("Yes");
	} main {

		Scanner sc = new Scanner(System.in);
		int n =sc.nextInt();
		int[] h = new int[100000001];
		boolean flag=false;
		for(int i=0;i<n;i++) {
			h[i]=sc.nextInt();
			if( i!=0 && h[i]>h[i-1] ) {
					h[i]--;
			}
		}
		for(int i=0;i<n;i++) {
			if(i!=0 && h[i]<h[i-1]) {
				System.out.println("No");
				return;
			}
		}
		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[] h = new int[100000001]; h new int[100000001] 100000001 boolean flag=false; flag false for(int i=0;i<n;i++) {
			h[i]=sc.nextInt();
			if( i!=0 && h[i]>h[i-1] ) {
					h[i]--;
			}
		} int i=0; int i=0; i 0 i<n i n i++ i++ i {
			h[i]=sc.nextInt();
			if( i!=0 && h[i]>h[i-1] ) {
					h[i]--;
			}
		} {
			h[i]=sc.nextInt();
			if( i!=0 && h[i]>h[i-1] ) {
					h[i]--;
			}
		} h[i]=sc.nextInt() h[i] h i sc.nextInt() sc.nextInt sc if( i!=0 && h[i]>h[i-1] ) {
					h[i]--;
			} i!=0 && h[i]>h[i-1] i!=0 i 0 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=0;i<n;i++) {
			if(i!=0 && h[i]<h[i-1]) {
				System.out.println("No");
				return;
			}
		} int i=0; int i=0; i 0 i<n i n i++ i++ i {
			if(i!=0 && h[i]<h[i-1]) {
				System.out.println("No");
				return;
			}
		} {
			if(i!=0 && h[i]<h[i-1]) {
				System.out.println("No");
				return;
			}
		} if(i!=0 && h[i]<h[i-1]) {
				System.out.println("No");
				return;
			} i!=0 && h[i]<h[i-1] i!=0 i 0 h[i]<h[i-1] h[i] h i 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 sc = new Scanner(System.in);
		int n =sc.nextInt();
		int[] h = new int[100000001];
		boolean flag=false;
		for(int i=0;i<n;i++) {
			h[i]=sc.nextInt();
			if( i!=0 && h[i]>h[i-1] ) {
					h[i]--;
			}
		}
		for(int i=0;i<n;i++) {
			if(i!=0 && h[i]<h[i-1]) {
				System.out.println("No");
				return;
			}
		}
		System.out.println("Yes");
	}
} public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		int n =sc.nextInt();
		int[] h = new int[100000001];
		boolean flag=false;
		for(int i=0;i<n;i++) {
			h[i]=sc.nextInt();
			if( i!=0 && h[i]>h[i-1] ) {
					h[i]--;
			}
		}
		for(int i=0;i<n;i++) {
			if(i!=0 && h[i]<h[i-1]) {
				System.out.println("No");
				return;
			}
		}
		System.out.println("Yes");
	}
} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		int n =sc.nextInt();
		int[] h = new int[100000001];
		boolean flag=false;
		for(int i=0;i<n;i++) {
			h[i]=sc.nextInt();
			if( i!=0 && h[i]>h[i-1] ) {
					h[i]--;
			}
		}
		for(int i=0;i<n;i++) {
			if(i!=0 && h[i]<h[i-1]) {
				System.out.println("No");
				return;
			}
		}
		System.out.println("Yes");
	}
}
