var currentPhoto = -1;

function showPhoto(index) {
	currentPhoto = index;
	if (currentPhoto >= photos.length) currentPhoto = 0;
	if (currentPhoto < 0) currentPhoto = photos.length - 1;
	document.getElementById("tourPhoto").src = photos[currentPhoto];
	document.getElementById("tourCaption").innerHTML = captions[currentPhoto];
}

showPhoto(0);