how can i obtain a cut off value in 5 point likert scale

how can i find a cut off value for attitude using a 5 point likert scale where i have 20 statements.The scale ranges from strongly agree, agree, neutral, disagree and strongly disagree, each with a value of 5, 4, 3, 2 and 1 respectively. And now i have to categorize it into 2 category by some cut off value into positive and negative. how can i do that? i have tried to take its median but i am being unable to. please teach me the proper way.