import java.util.*;
class Main{
public static void main(String[] args){
Scanner sc=new Scanner(System.in);
int n=sc.nextInt();
int[] nums=new int[n];
for(int i=0;i<n;i++)nums[i]=sc.nextInt();
for(int i=1;i<n;i++){
if(nums[i-1]<nums[i])nums[i]--;
else if(nums[i-1]>nums[i]){System.out.println("No");
return;}
}
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