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];
        for (int i = 0; i < h.length; i++) {
            h[i] = sc.nextInt();
        }
        boolean ok = true;
        for (int i = h.length - 2; i >= 0; i--) {
            if (h[i] - h[i + 1] == 1) {
                h[i]--;
            } else if (h[i] > h[i + 1]) {
                ok = false;
            }
        }
        if (ok) {
            System.out.println("Yes");
        } else {
            System.out.println("No");
        }
        sc.close();
    }
}
/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