function showp1()
 {
    document.getElementById("p10").style.display="block";
    document.getElementById("p21").style.display="block";
    document.getElementById("p20").style.display="none";
    document.getElementById("p11").style.display="none";
    document.getElementById("n1").style.display="block";
    document.getElementById("n2").style.display="none";
}
function showp2()
{
    document.getElementById("p11").style.display="block";
    document.getElementById("p20").style.display="block";
    document.getElementById("p21").style.display="none";
    document.getElementById("p10").style.display="none";
    document.getElementById("n2").style.display="block";
    document.getElementById("n1").style.display="none";
}