calcGrima - Java class

public class calcGrima
{
    public double killgrima(int HP, int zahl)
    {
        if(HP<=0){
            return 1.0;
        }
        if(zahl<1){  // KJELLE
            double probZeroDmg = killgrima(HP, zahl+1) * (0.84 * 0.2278 + 0.16 * 0.2278 * 0.2278);
            double prob4Dmg = killgrima(HP-4, zahl+1) * (0.84 * 0.7722 * 0.67 * 0.38 + 0.16 * 0.7722 * 0.38 * 0.2278);
            double prob8Dmg = killgrima(HP-8, zahl+1) * (0.84 * 0.7722 * 0.67 * 0.62 + 0.16 * 0.7722 * 0.62 * 0.2278);
            double prob9Dmg = killgrima(HP-9, zahl+1) * (0.84 * 0.7722 * 0.33 * 0.38 + 0.16 * 0.2278 * 0.7722 * 0.38);
            double prob18Dmg = killgrima(HP-18, zahl+1) * (0.84 * 0.7722 * 0.33 * 0.62 + 0.16 * 0.2278 * 0.7722 * 0.62);

            double prob13Dmg = killgrima(HP-13, zahl+1) * 0.16 * 0.7722 * 0.7722 * 0.38 * 0.38;
            double prob17Dmg = killgrima(HP-17, zahl+1) * 0.16 * 0.7722 * 0.7722 * 0.62 * 0.38;
            double prob22Dmg = killgrima(HP-22, zahl+1) * 0.16 * 0.7722 * 0.7722 * 0.38 * 0.62;
            double prob26Dmg = killgrima(HP-26, zahl+1) * 0.16 * 0.7722 * 0.7722 * 0.62 * 0.62;

            return probZeroDmg + prob4Dmg + prob8Dmg + prob9Dmg + prob18Dmg + prob13Dmg + prob17Dmg + prob22Dmg + prob26Dmg;
        }else if(zahl<3){ //MORGAN, except DSes
            return 0.1326 * killgrima(HP, zahl+1) + 0.8674 * (0.33 * killgrima(HP-15,zahl+1)+0.67*killgrima(HP-10,zahl+1));
        }else if(zahl<7) //SULLY, except DSes
        {
            return 0.38 * killgrima(HP-3, zahl+1) + 0.62 * killgrima(HP-7, zahl+1);
        }else if(zahl<9) //KJELLE DSes
        {
            return 0.5247 * 0.36 * killgrima(HP-8, zahl+1) + (0.64 + 0.36 * 0.4753) * killgrima(HP, zahl+1);
        }else if(zahl<13) // MORGAN DSes
        {
            return 0.7444 * 0.37 * killgrima(HP-10, zahl+1) + (0.63 + 0.37*0.2556) * killgrima(HP, zahl+1);
        }else
        {
            return 0.0;
        }
    }
}