Please Fix This Issue About Contacts backup

[muznybozz]

Hi my device is iPhone 4S
iOS 8.0.2 problem is some of my apps like whatsappp Facebook stops suddenly. So I decided to restore it completely to iOS 8.0.2. Full restore.
But I may lose my contacts which is over 500.
I want to know all the methods to backup my contacts and restore it completely to iPhone.Plzz help mme.