import java.util.*;
import java.lang.*;

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