public class Solution {

    public static void main(String[] args) {
        double mean = 20;
        double stdDeviation = 2;
        double x1 = 19.5, x2 = 22;

        double result1 = probability(mean, stdDeviation, x1);
        double probLe20 = 0.5; // le mean == ge mean == 50%
        double result2 = probability(mean, stdDeviation, x2) - probLe20;

        System.out.println(round(result1));
        System.out.println(round(result2));
    }
		
    static double probability(double mean, double stdDeviation, double x) {
        final double z = calcZ(mean, stdDeviation, x);
        return 1 - (1 + erf(z)) / 2;
    }
		
    static double calcZ(double mean, double stdDeviation, double x) {
        return (mean - x) / (stdDeviation * Math.sqrt(2));
    }
		
    static double erf(double z) {
        double sum = 0;
        for (int n = 0; n < 11; n++) {
            double t = z / (2 * n + 1);
            for (int i = 1; i <= n; i++)  t *= -z * z / i;
            sum += t;
        }
        return 2 / Math.sqrt(Math.PI) * sum;
    }
		
    static double round(double v) {
        return Math.round(v * 1000) * 1d / 1000;
    }
}