n = gets.to_i

l = gets.to_s.chop.split(" ").map{|i|i.to_i}

xy = gets.to_s.chop.split(" ").map{|i|i.to_i}

x = xy[0] < 0 ? xy[0] * -1 : xy[0]  
y = xy[1] < 0 ? xy[1] * -1 : xy[1]            

sum = x+y

step = -1
               
(l.size).times{|i|    
  if l[i] == sum  
    step = 1
    break          
  end              
  (l.size-1-i).times{|j| 
    if l[i] + l[i+j+1] == sum || (l[i] - l[i+j+1]).abs == sum
      step = 2                                               
    end              
  }                                      
  if step == 1 
    break
  end              
}                                        

puts step