var value = 0 ;
function comedown(value)
{
height = document.getElementById("post").scrollHeight ;
if ( height >= 270 && height+value > 0 )
	{
	document.getElementById("post").style.marginTop = value+"px";
	}
}

function comeup(value)
{
height = document.getElementById("post").scrollHeight ;
if ( height >= 270 && value <= 0 )
	{
	document.getElementById("post").style.marginTop = value+"px";
	}
}


function scrollmeup()
{
value = value+150;
if ( value <= 0 ) { comeup(value); } else { value = 0 ; }
}

function scrollmedown()
{
value = value-150;
if ( value*(-1) < document.getElementById('post').scrollHeight ) { comedown(value); } else { value = value+150 ;}
}