Help Javascript - Script simple défilement slider

<div id="Presentation" class="tabcontent mySlides" style="display: block;">
bla bla bla
</div>
<div id="Contact" class="tabcontent mySlides">
bla bla bla
</div>
<div id="Service" class="tabcontent mySlides">
bla bla bla
</div>

<div class="tab" id="tabDot">
<button class="tablinks active" onclick="openSlider(event, 'Presentation')"></button> <button class="tablinks" onclick="openSlider(event, 'Contact')">
</button>
<button class="tablinks" onclick="openSlider(event, 'Service')"></button> </div>

<script>
function openSlider(evt, sliderName) {
var i, tabcontent, tablinks;
tabcontent = document.getElementsByClassName("tabcontent");
for (i = 0; i < tabcontent.length; i++) {
tabcontent[i].style.display = "none";
}
tablinks = document.getElementsByClassName("tablinks");
for (i = 0; i < tablinks.length; i++) {
tablinks[i].className = tablinks[i].className.replace(" active", "");
}
document.getElementById(sliderName).style.display = "block";
evt.currentTarget.className += " active";
}

var slideIndex = 0;
carousel();

function carousel() {
var i;
var x = document.getElementsByClassName("mySlides");
for (i = 0; i < x.length; i++) {
x[i].style.display = "none";
}
slideIndex++;
if (slideIndex > x.length) {
slideIndex = 1
}
x[slideIndex-1].style.display = "block";
setTimeout(carousel, 5000);
}
</script>