I want to picture 5s change next picture, but I can't make this work.

```
<div class="g-carousel" id="m-carousel">
    <a href="http://open.163.com/" class="pciture" target="_blank"><img src="imag/banner1.jpg" ></a>
    <a href="http://study.163.com/" class="pciture two" target="_blank" style="display:none"><img src="imag/banner2.jpg" ></a>
    <a href="http://www.icourse163.org/" class="pciture three" target="_blank" style="display:none"><img src="imag/banner3.jpg" ></a>
    <div class="button">
        <i class="checked"></i><i></i><i></i>
    </div>
</div>
<script type="text/javascript">
    function showpic() {
        var carousel = document.getElementById("m-carousel")
        var pciture = carousel.getElementsByClassName("pciture");
                for (var i=0 ; i < pciture.length; i++)
                    if (i>2) i=0;
                pciture[i].style.display="none";
                pciture[i+1].style.display="block";

        }
        window.onload=function function_name(argument) {
            setInterval("showpic()",5000);
        }   
</script>

```