// editor1
import java.util.*;
class main{
    public static void main(String[]args){
        Scanner sc=new Scanner(System.in);
        int a=sc.nextInt();
        if(a<=0){
            System.out.println("Invalid input");
            return;
        }
        int[]ar=new int[a];
        for(int i=0;i<a;i++){
            ar[i]=sc.nextInt();
        }
        
        int num=1;
        
        boolean found=false;
        while(true){
            for(int i=0;i<a;i++){
                if(ar[i]==num)
                {
                    found=true;
                    num++;
                    k++;
                }
                
                num++;
            }
            break;
        }
        if(found){
            System.out.println("Yes");
            
        }
        
        else{
        System.out.println("No");
        
    }}
}