#hackerunderground puzzle

def dupefinder(lister):
    '''Function to find first duplicate in a list; Variable to pass
     to this function should be of type "list" '''
    listerdupe = sorted(lister)
    for index,item in enumerate(listerdupe):
        if item == listerdupe[index+1]:
            print('First duplicate number is {0}'.format(item))
            return item