import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] h = new int[n];
        int[] d = new int[n];
        for (int i = 0 ; i < n ; i++) {
            h[i] = sc.nextInt();
        }
        if (n == 1) {
            System.out.println("Yes");
            return;
        }
        h[0] -= 1;
        for (int i = 0 ; i < n - 1 ; i++) {
            if (h[i] - h[i + 1] >= 1) {
                System.out.println("No");
                return;
            }
            if (h[i] < h[i + 1]) {
                h[i + 1] -= 1;
            }
        }

        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