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<N;i++) {
		H[i]=sc.nextInt();
	}
	sc.close();

	for(int i=N-1;i>0;i--) {
		if(H[i]==H[i-1]-1) {
			H[i-1]--;
		}else if(H[i]<H[i-1]-1) {
			System.out.println("No");
			System.exit(0);
		}
	}
	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