import java.util.Scanner;
 
public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		sc.next();
		int a = Integer.parseInt(sc.next());
		int current = a;
		int next = 0;
		boolean can = true;
		int sa = 0;
		String result = "Yes";
		while(sc.hasNext()) {
			next = Integer.parseInt(sc.next());
			if(can) current--;
			sa = current - next;
			if(sa>0) {
				result = "No";
				break;
			}
			if(current<next) {
				can = true;
			}else {
				can = false;
			}
			current = next;
		}
		System.out.println(result);
	}
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz