A 3-year-old child has been brought to a hospital with complaints of pain in the legs, fever, and loss of appetite. Objectively: pale skin and mucosa, hemorrhagic rash. Lymph nodes are enlarged, painless, dense and elastic, not matted together. Bones, joints, and abdomen are painful. The liver and spleen are enlarged. Hemogram: Hb — 88 g/L, color index — 1.3, platelets — 80 • 109/L, leukocytes — 25.8 •109/L, lymphoblasts — 70%, ESR — 52 mm/hour. Make the provisional diagnosis: