import java.util.*;

public class Main {
    public static void main(String args[]) {
    Scanner read = new Scanner(System.in);
    int n = read.nextInt();
    int d[] = new int[n];
    d[0] = read.nextInt()-1;
    boolean ban=true;
    for(int i=1; i<n; i++){
        d[i]=read.nextInt();
        if(d[i-1] > d[i]){
            ban=false;
            break;
        }
        if(d[i-1] < d[i])
            --d[i];
    }
    
        if(ban)
           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