import java.util.Scanner;
public class Main{
 public static void main(String[] args){
   Scanner sc = new Scanner(System.in);
   int N = sc.nextInt();
   int[] Hi = new int[N];
   for(int i =0;i<N;i++)
   {
   Hi[i] = sc.nextInt();
   }
   int outcount=0;
   for(int k=0;k<N-1;k++)
   {
    if( Hi[k] < Hi[k+1] )
    {
    outcount=0;
    }
    else if (Hi[k] == Hi[k+1]){}
    else
    {
    if(Hi[k] == Hi[k+1]+1) outcount++;
    else outcount=2;
    }
    
    if(outcount==2) break;
   }
    if(outcount==2) System.out.println("No");
    else System.out.println("Yes");
 }
}
/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