import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		final int N = scan.nextInt();
		long[] h = new long[N];
		for(int i = 0; i < N; i++) {
			h[i] = scan.nextLong();
		}
		scan.close();
		boolean flg = true;
		// 末尾から見ていく
		for(int i = N - 2; i >= 0; i--) {
			if(h[i] - h[i + 1] == 1) {
				h[i]--;
			}else if(h[i] - h[i + 1] >= 2 ) {
				flg = false;
				break;
			}
		}
		if(flg) {
			System.out.println("Yes");
		}else {
			System.out.println("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