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

public class Main {
    static void answer(boolean ans){
        System.out.println(ans ? "Yes" : "No");
        System.exit(0);
    }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        long[] H = new long[N+1];
        for(int n=1; n<=N; n++) H[n]=sc.nextLong();

        for(int n=1; n<=N; n++){
            if(H[n-1] > H[n]) answer(false);
            if(H[n-1] < H[n]) H[n]--;
        }
        answer(true);
    }
}

/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