A 35-year-old male presents with high fever and pruritus (skin itching) for half a month, along with right cervical and supraclavicular lymphadenopathy (enlarged lymph nodes) that is adherent to each other and shows no tenderness. Lab results: hemoglobin (Hb) 90g/L, white blood cell (WBC) count 10×10<sup>9</sup>/L (neutrophils 66%, lymphocytes 24%). Bone marrow smear reveals Reed-Sternberg cells (R-S cells). The most likely diagnosis is: