Sample Size & Confidence Interval

I need someone to help me with the problem listed below. I have read and re-read it and I don't think we can complete this problem with the information given because of the unknown number of students in the university. Am I right?

Preliminary estimates suggest that about 58% of students at a state university favor implementing an honor code. To obtain a 95% confidence interval of the proportion of all students at the university favoring the honor code, what is the minimum sample size needed if the total width of the confidence interval must be less that 5 percentage points (i.e. the confidence interval should extend at most 2.5 percentage points above the below the sample proporation)?