//<!--
var first = 1;
var last = 19;
var current = 1;

function nextPicture() {
    // Hide current picture
    var object = document.getElementById('slide' + current);
    object.style.display = 'none';
    
    // Show next picture, if last, loop back to front
    if (current == last) { current = 1; }
    else { current++ }
    var object = document.getElementById('slide' + current);
    object.style.display = 'block';
}

function previousPicture() {
    // Hide current picture
    var object = document.getElementById('slide' + current);
    object.style.display = 'none';
    
    if (current == first) { current = last; }
    else { current--; }
    var object = document.getElementById('slide' + current);
    object.style.display = 'block';
}
// -->