import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        sc.nextLine();
        String line = sc.nextLine();
        int[] h = new int[n];
        String[] ll = line.split(" ");

        for (int i = 0; i < n; i++) {
            h[i] = Integer.parseInt(ll[i]);
        }

        boolean isLiner = true;
        int max = h[0];
        for (int i = 0; i < n; i++) {
            if(max > h[i]){
                isLiner = false;
            }

            if(max < h[i] - 1){
                max = h[i] - 1;
            }

        }

        if (isLiner) {
            System.out.println("Yes");
        } else {
            System.out.println("No");
        }
        return;
    }
}

/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