# Write a Python Set difference to find lost element from a duplicated array 
 # Function to find lost element from a duplicate
# array
  
def lostElement(A,B):
      
     # convert lists into set
     A = set(A)
     B = set(B)
  
     # take difference of greater set with smaller
     if len(A) > len(B):
         print (list(A-B))
     else:
         print (list(B-A))
  
# Driver program
if __name__ == "__main__":
    A = [1, 4, 5, 7, 9]
    B = [4, 5, 7, 9]
    lostElement(A,B)