function ecrire_cookie(nom, valeur, expires) {
    document.cookie = nom+"="+escape(valeur)+((expires==null) ? "" : ("; expires="+expires.toGMTString()));
}

function arguments_cookie(offset) {
    var endstr = document.cookie.indexOf (";", offset);
    if (endstr == -1) endstr = document.cookie.length;
    return unescape(document.cookie.substring(offset, endstr));
}

function lire_cookie(nom) {
    var arg = nom+"=";
    var alen = arg.length;
    var clen = document.cookie.length;
    var i = 0;

    while (i < clen){
        var j = i+alen;
        if (document.cookie.substring(i, j) == arg)
            return arguments_cookie(j);

        i = document.cookie.indexOf(" ",i)+1;
        if (i == 0) break;
    }

    return null;
}

function random_bkg(a) {
    var max = a.length;

    var random = (Math.floor((Math.random() * max)));

    ecrire_cookie("random", random);

    return a[random];
}