Displaying Alternative Positive and Negative Numbers in JavaScript

<!DOCTYPE html>
<html>
    <body>
        <p id="displayseries"></p>
        <input type = "text" id ="UserInput" />
        <button type="button" onClick="MakeSeries()"> Enter number upto which series has to be made.</button>
        <script>
            function MakeSeries(){
            var x = document.getElementById("UserInput").value;
            var text = "";
            var i;var j = -2;
            for (i = 1; i < x; i++) {
               text += "+" + i + "
             <br>";
              i = i+1;
            while (j > -x) {
              text +=  j + "
                <br>";
                j = j-2;
                break;
            }}
            document.getElementById("displayseries").innerHTML = text;
         }
        </script>
    </body>
</html>