Generate a topic word for the given sentence. A topic word is usually the name of a person, place, animal, concept or object the sentence is focusing on.

Example Input: mother teresa (born agnes gonxha bojaxhiu, 26 august 1910 – 5 september 1997), was a roman catholic nun who started the missionaries of charity and won the nobel peace prize in 1979 for her work with people.for over forty years, she took care of needs of those without money, those who were sick, those without parents, and those dying incalcutta (kolkata), guided in part by the ideals of saint francis of assisi.
Example Output: mother teresa

Example Input: dakota johnson (born october 4, 1989 in austin, texas) is an american actress and model.
Example Output: dakota johnson

Example Input: a tension headache is a common form of headache.
Example Output:
tension headache