Constructing n-grams – we make a set of n-grams out of consecutive words. A negation (such as “no” and “not”) is attached to a word which precedes it or follows it. For example, a sentence “I do not like fish” will form two bigrams: “I do+not”, “do+not like”, “not+like fish”. Such a procedure allows to improve the accuracy of the classification since the negation plays a special role in an opinion and sentiment expression( Wilson et al., 2005).