function gamma(x){
	var p = [0.99999999999980993, 676.5203681218851, -1259.1392167224028,
		771.32342877765313, -176.61502916214059, 12.507343278686905,
		-0.13857109526572012, 9.9843695780195716e-6, 1.5056327351493116e-7];
				
	var g = 7;
	if(x < 0.5){
		return Math.PI / (Math.sin(Math.PI * x)*gamma(1-x));
	}

	x -= 1;
	var a = p[0];
	var t = x+g+0.5;
	for(var i = 1; i < p.length; i++){
		a += p[i]/(x+i);
	}

	return Math.sqrt(2*Math.PI)*Math.pow(t, x+0.5)*Math.exp(-t)*a;
}