	import java.util.*;

	public class Main{
			
			public static void main(String args[]){
			
				Scanner sc = new Scanner(System.in);
				int n = sc.nextInt();
				
				int heights[] = new int[n];
				
				for(int i = 0; i < n; i++){
					
					heights[i] = sc.nextInt();
					
				}
				
				int flag = 1;
				
				for(int i = n-1; i > 0 ; i--) {
						
					if(heights[i] < heights[i-1]){

						heights[i-1]-=1;
						
						if(heights[i] < heights[i-1]){
	
							flag = 0;
							break;
						
						} else {
							
							continue;		
						
						}
						
					} else {

							continue;
				
					}						
				
				}
					
					if(flag == 1){
						
						System.out.println("Yes");
						
					} else {
						
						System.out.println("No");
						
					}
				
			
			}
	}
/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