function changeBg() {
	document.body.style.backgroundImage = 'url(img/corporate_top_main.jpg)';
}
function changeBg2() {
	document.body.style.backgroundImage = 'url(img/private_top_main.jpg)';
}
function recover() {
	document.body.style.backgroundImage = 'url(img/corporate_top_main.jpg)';
}