Plug your device to computer, run iTunes and in your devices section click on your device and then click on "Info" tab. Then in the field in front of "sync contacts with" choose "windows contacts".
Press sync and wait for couple of seconds.
Now press this key on keyboard (windows key) + R and "run" window will pop up.
Type "wab" and press enter. Then click on "export" top right corner.
Choose "CSV" and press enter. Then specify a path and click on next.
Check everyone of them (remember to scroll down) and click on finish.
Now you have a CSV file which can be opened using Microsoft excel, you should store it somewhere safe. Now let's say you have recently reinstalled your OS and also restored your iOS! Go to next step.
To import the contacts to device you shoud do exactly as i said but in reverse! So go to "Run" type "wab" and this time click on "import" and choose the CSV file. Plug your device and go to iTunes...
Click on "Info" and choose Sync with "Windows Contacts" and press sync. Now all your contacts are back! Have fun!