apply experession if checked checkbox is more than one

http://ift.tt/1Ep87xe

<li ng-repeat="d in data"><input type="checkbox"/>{{$index}}</li>
<button ng-show="checkismorethanone">Save</button>

I can't use ng-model because it will check all the checkbox. How can I know if there's any of the checkbox checked? I want to show the save button if anyone of the checkbox is checked, or hide the button if no more button is checked.