4
90 91 90 91
 4
54 54 54 55
 10
55 39 93 42 97 40 36 38 11 97
 3
90 39 98
 5
21 57 40 94 17
 8
46 4 30 85 52 6 84 13
 6
47 100 96 2 96 43
 4
61 28 3 81
 5
14 91 91 91 84
 3
22 23 24
 1
13
 9
13 80 13 38 98 85 11 73 74
 10
95 51 52 8 44 39 77 17 96 88
 3
40 40 40
 4
16 17 17 18
 3
68 67 67
 4
83 100 81 75
 9
71 71 70 70 71 70 69 70 71
 10
9 9 9 10 10 9 8 8 9 9
 6
87 86 86 86 85 86
 5
64 63 63 62 61
 3
76 9 12
 4
61 60 60 60
 7
23 37 39 8 72 31 85
 10
67 67 67 67 67 67 67 67 67 67
 4
92 18 29 93
 4
14 15 15 16
 10
79 84 22 38 23 22 33 42 13 96
 7
20 21 95 73 49 98 53
 10
28 61 23 73 61 33 45 55 18 43
 9
15 14 14 13 13 12 13 13 14
 5
46 46 47 46 45
 7
35 91 87 78 17 71 63
 3
69 26 73
 10
16 17 16 15 14 15 16 17 16 15
 9
95 7 97 61 90 7 30 65 39
 10
2 83 18 65 58 95 37 51 86 47
 6
59 59 60 60 59 58

YES YES NO NO NO NO NO NO NO YES YES NO NO YES YES YES NO YES YES YES YES NO YES NO YES NO YES NO NO NO YES YES NO NO YES NO NO YES
        import java.io.*;
        import java.util.StringTokenizer;
        import java.util.*;
        import java.math.*;
        import java.lang.Integer;
         
        public class Solution {
        	
        	
        	public static String sort(Integer[] arr) {
        		Integer n= arr.length;
        		Integer[] narr=  new Integer[n];
        		for (int i = 0; i < n; i++) {
        		    narr[i]=arr[i];
        		}
        		Integer[] oarr=  new Integer[n];
        		for (int i = 0; i < n; i++) {
        		    oarr[i]=arr[i];
        		}
        		
        			
        		Integer res;
        		Integer resindex;
        		Boolean check;
        		
        		for (int i = 0; i < n; i++) {
        		    
        		    check=true;
        	
        	    while(check){
        	        check=false;
        		for (int j = 1; j < n-i; j++) {
        		    //System.out.println(narr[j]);
        		    if(narr[j]>=narr[j-1]+2){
        		        check=true;
        		        narr[j]=narr[j]-1;
        		        narr[j-1]=narr[j-1]+1;
        		    }
        		    if(narr[j-1]>=narr[j]+2){
        		        check=true;
        		        narr[j]=narr[j]+1;
        		        narr[j-1]=narr[j-1]-1;
        		    }
        		}
        	    }
        	    
        	    
        	    
        	    //System.out.println("here");
        			    res=0;
        			    resindex=0;
        			    for (int j = 0; j < n-i; j++) {
        			        if(narr[j]>res){
        			            res=narr[j];
        			            resindex=j;
        			        }
        			        //System.out.println(resindex);
        			    }
        			    
        			    for (int j = resindex; j < n-i-1; j++) {
        			        narr[j]=narr[j+1];
        			        //System.out.println(resindex);
        			    }
        			
        			    narr[n-i-1]=res;
        		
        		 //System.out.println("here");
        			
        		}
        		
        		
        		Arrays.sort(oarr);
        		//for (int j = 0; j < n; j++) {
        	    //System.out.println(oarr[j]);
        	    //}
        		
        		if(Arrays.equals(narr, oarr)){
        		    return "YES";
        		}else{
        		    return "NO";
        		}
        		
        		
        	}
        	
        	
        	public static void main(String[] args) throws Exception {
        		FastScanner cin = new FastScanner(System.in);
        		Integer n =cin.nextInt();
        		
        		Integer[] arr= new Integer[n];
        		
        		for (int i = 0; i < n; i++) {
        			arr[i]=cin.nextInt();
        			
        		}
        		
        		
        		
        		System.out.println(sort(arr));
        		
        		
        		
        	}
         
        	static class FastScanner {
        		private BufferedReader reader = null;
        		private StringTokenizer tokenizer = null;
         
        		public FastScanner(InputStream in) {
        			reader = new BufferedReader(new InputStreamReader(in));
        			tokenizer = null;
        		}
         
        		public String next() {
        			if (tokenizer == null || !tokenizer.hasMoreTokens()) {
        				try {
        					tokenizer = new StringTokenizer(reader.readLine());
        				} catch (IOException e) {
        					throw new RuntimeException(e);
        				}
        			}
        			return tokenizer.nextToken();
        		}
         
        		public String nextLine() {
        			if (tokenizer == null || !tokenizer.hasMoreTokens()) {
        				try {
        					return reader.readLine();
        				} catch (IOException e) {
        					throw new RuntimeException(e);
        				}
        			}
         
        			return tokenizer.nextToken("\n");
        		}
         
        		public long nextLong() {
        			return Long.parseLong(next());
        		}
         
        		public int nextInt() {
        			return Integer.parseInt(next());
        		}
         
        	}
        }