function switchBlock()
{
    var i=0;
    var div;
    var count=0;

    while (document.getElementById( 'block_' + count) != null)
    {
        count++;
    }
    count--;

    while (document.getElementById( 'block_' + i) != null)
    {
        div = document.getElementById(  'block_' + i);

        if(div.style.display=='block')
        {
            div.style.display='none';
            if (i==count)
            {
                i=0;
            }
            else
            {
                i++;
            }
            div = document.getElementById('block_' + i);
            div.style.display='block';

            break;
        }

        i++;
    }
}