function check(ad)
{
	var ch=ad.value;
	if(isNaN(ch))
	{
		var df=ch.substring(0,(ch.length-1))
		ad.value=df;
	}	
}



function neg()
{
	var n=parseInt(document.nb.b1.value);
	var r=parseInt(document.nb.b2.value);
	var p=parseFloat(document.nb.b3.value);
	
	if(p>1)
	{
		alert("The probability of success must be between 0 and 1");
	}
	else if(r>n)
	{
		alert("Number of success r should be less than number of events n");
	}
	else
	{
		var a=n-1;
		var b=r-1;
		
//(n-1)!
		var z=1;
		for(var i=a; i>=1; i--)
		{
			z=z*i;
		}
		
//(r-1)! 
		var t=1;
		for(var j=b; j>=1; j--)
		{
			t=t*j;
		}
		
//((n-1)-(r-1))! 
		var x=a-b;
		var s=1;
		for(k=x; k>=1; k--)
		{
			s=s*k;
		}
		
		var c=z/s;
		
//((n-1)!/((n-1)-(r-1))!)/(r-1)! = d ; p^r = e ; 1-p=f  ; n-r=g 
		var d=c/t;
		var e=Math.pow(p,r);
		var f=1-p;
		var g=n-r;
		var h=Math.pow(f,g);
		var res=d*e*h;
		document.nb.nbi.value=Math.round((res)*100000)/100000;
	}
}