import java.util.*;
class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int[] h = new int[n];
        boolean ans = true;
        for(int i =0;i<n;i++){
            h[i] = Integer.parseInt(sc.next());
        }
        int tmp = h[0];
        for(int i =1;i<n;i++){
            if(tmp<=h[i]-1){
                tmp = h[i]-1;
            } else if(tmp<=h[i]){
                tmp = h[i];
            } else {
                ans = false;
                break;
            }
        }
        System.out.println(ans?"Yes":"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