What proportion of secretaries of Fortune 500 companies has a personal computer at his or her workstation?

What proportion of secretaries of Fortune 500 companies has a personal computer at his or her workstation? You want to answer this question by conducting a random survey. How large a sample should you take if you want to be 95% confident of the results and you want the error of the confidence interval to be no more than .05? Assume no one has any idea of what the proportion actually is.Round your answer up to the nearest integer.