Cannot sample enough valid points. (more)

\[\left(\left(\left(\sqrt{x + 1} - \sqrt{x}\right) + \left(\sqrt{y + 1} - \sqrt{y}\right)\right) + \left(\sqrt{z + 1} - \sqrt{z}\right)\right) + \left(\sqrt{t + 1} - \sqrt{t}\right)\]
\left(\left(\left(\sqrt{x + 1} - \sqrt{x}\right) + \left(\sqrt{y + 1} - \sqrt{y}\right)\right) + \left(\sqrt{z + 1} - \sqrt{z}\right)\right) + \left(\sqrt{t + 1} - \sqrt{t}\right)
double f(double x, double y, double z, double t) {
        double r21279000 = x;
        double r21279001 = 1.0;
        double r21279002 = r21279000 + r21279001;
        double r21279003 = sqrt(r21279002);
        double r21279004 = sqrt(r21279000);
        double r21279005 = r21279003 - r21279004;
        double r21279006 = y;
        double r21279007 = r21279006 + r21279001;
        double r21279008 = sqrt(r21279007);
        double r21279009 = sqrt(r21279006);
        double r21279010 = r21279008 - r21279009;
        double r21279011 = r21279005 + r21279010;
        double r21279012 = z;
        double r21279013 = r21279012 + r21279001;
        double r21279014 = sqrt(r21279013);
        double r21279015 = sqrt(r21279012);
        double r21279016 = r21279014 - r21279015;
        double r21279017 = r21279011 + r21279016;
        double r21279018 = t;
        double r21279019 = r21279018 + r21279001;
        double r21279020 = sqrt(r21279019);
        double r21279021 = sqrt(r21279018);
        double r21279022 = r21279020 - r21279021;
        double r21279023 = r21279017 + r21279022;
        return r21279023;
}