A patient comes to ED with fever and headache. On examination he has neck stiffness. CSF analysis was done:- Parameter Finding Normal range Glucose (mg/dl) 55 50-80 Protein (g/L) 0.50 0.18-0.45 ICT (cmH2O) 35 5-20 WBC 25 (predominantly lymphocytes) <5 Most likely diagnosis is-