double N(double x)
{
	int neg = (x<0);
	if(neg) x *= -1;
	double k(1/(1+0.2316419*x));
	double y=((((1.330274429*k-1.821255978)*k+1.781477937)*k-0.356563782)*k+0.319381530)*k;
	y = 1.0 - 0.398942280401*exp(-0.5*x*x)*y;
	return (1-neg)*y + neg*(1-y);
}