<img class="mySlides" src="img_fjords.jpg">
<img class="mySlides" src="img_lights.jpg">
<img class="mySlides" src="img_mountains.jpg">
<img class="mySlides" src="img_forest.jpg">


<button class="w3-button w3-display-left" onclick="plusDivs(-1)">&#10094;</button>
<button class="w3-button w3-display-right" onclick="plusDivs(+1)">&#10095;</button>


var slideIndex = 1;
showDivs(slideIndex);

function plusDivs(n) {
    showDivs(slideIndex += n);
}

function showDivs(n) {
    var i;
    var x = document.getElementsByClassName("mySlides");
    if (n > x.length) {slideIndex = 1}
    if (n < 1) {slideIndex = x.length} ;
    for (i = 0; i < x.length; i++) {
        x[i].style.display = "none";
    }
    x[slideIndex-1].style.display = "block";
}