var current = 0;

function first() {
current = 0;
document.images.show.src = cat + '00.jpg';
document.getElementById('desc').childNodes[0].nodeValue = (current+1) + '/' + (ostatnia+1)
}

function last() {
current = ostatnia;
if (current<=9) document.images.show.src = cat + '0' + (current) + '.jpg';
else document.images.show.src = cat + (current) + '.jpg';
document.getElementById('desc').childNodes[0].nodeValue = (current+1) + '/' + (ostatnia+1)
}

function next() {
if ((current+1)<=ostatnia) {
if (current<9) document.images.show.src = cat + '0' + (current+1) + '.jpg';
else document.images.show.src = cat + (current+1) + '.jpg';
current += 1;
document.getElementById('desc').childNodes[0].nodeValue = (current+1) + '/' + (ostatnia+1)
   }
else first();
}

function previous() {
if (current-1 >= 0) {
if (current<11) document.images.show.src = cat + '0' + (current-1) + '.jpg';
else document.images.show.src = cat + (current-1) + '.jpg';
current -= 1;
document.getElementById('desc').childNodes[0].nodeValue = (current+1) + '/' + (ostatnia+1)
   }
else last();
}