function getRandom(min_random, max_random) {
    var range = max_random - min_random + 1;
    return Math.floor(Math.random()*range) + min_random;
}

function getRandomBg() {
	var bg_num = getRandom(1, 7);
	var header_logo = document.getElementById('header_logo_m');
	header_logo.className = 'header_logo_m_' +  bg_num;
}