A 60-year-old man complains of frequent painful difficulty urinating, intermittent urine stream. Urination up to 5 times at night. After exercise notesblood impurities in the urine. Rectally established: the prostate is enlarged, densely elastic, painless, without knots. It is observed in urine; specific weight - 1020, protein - 0,1 g/l, leukocytes - 20-30 in p / z, erythrocytes - 10-20 in p / z. Which method of examination is paramount?