#Your optional code here

#You can import some modules or create additional functions

def checkio(data):

#Your code here

#It's main function. Don't remove this function

#It's used for auto-testing and must return a result for check.

data1 = []

for i in range(len(data)):

if data.count(data[i]) > 1:

data1.append(data[i])

#replace this for solution

return data1

#Some hints

#You can use list.count(element) method for counting.

#Create new list with non-unique elements

#Loop over original list

if __name__ == "__main__":

#These "asserts" using only for self-checking and not necessary for auto-testing

assert isinstance(checkio([1]), list), "The result must be a list"

assert checkio([1, 2, 3, 1, 3]) == [1, 3, 1, 3], "1st example"

assert checkio([1, 2, 3, 4, 5]) == [], "2nd example"

assert checkio([5, 5, 5, 5, 5]) == [5, 5, 5, 5, 5], "3rd example"

assert checkio([10, 9, 10, 10, 9, 8]) == [10, 9, 10, 10, 9], "4th example"