function random_image(num1,num2) {
        if((num1 - num2) > 0)   {
                var big = num1
                var small = num2
        } else  {
                var big = num2
                var small = num1
        }
        var range = big - small + 1
        var number = Math.floor(Math.random()*range) + small
        return(number)
}

function random_img()    {
        var img_src = "images/top_img/top_img" + random_image(1,5) + ".jpg"
        document.write("<IMG SRC='" + img_src + "'>")
}

random_img()