A 62-year-old man complains about a painless formation on his tongue that appeared several months ago. Objectively: there is a big number of carious and completely decayed teeth, a painless whitish formation 10х5 mm large with irregular surface in form of verrucas on the lateral surface of tongue. Histological examination revealed thickening of corneous layer of epithelium with intermittent cornification. What is the most probable diagnosis?