I am trying to write a function that returns a function which can be invoked twice(and the result of that is gonna be added together) but not more than twice. Also the result must be isNan as 

```
function twice(func) {
  var newFun=function(){
    for (var i=0; i<=2; i++){
      func();
    }
  }
  return newFun;
}

allReturns = twice(function() {
  return 4
});
var result=allReturns()+allReturns()+allReturns();  

```

Any suggestions? Thanks!!