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 r420839 = x;
        double r420840 = 1.0;
        double r420841 = r420839 + r420840;
        double r420842 = sqrt(r420841);
        double r420843 = sqrt(r420839);
        double r420844 = r420842 - r420843;
        double r420845 = y;
        double r420846 = r420845 + r420840;
        double r420847 = sqrt(r420846);
        double r420848 = sqrt(r420845);
        double r420849 = r420847 - r420848;
        double r420850 = r420844 + r420849;
        double r420851 = z;
        double r420852 = r420851 + r420840;
        double r420853 = sqrt(r420852);
        double r420854 = sqrt(r420851);
        double r420855 = r420853 - r420854;
        double r420856 = r420850 + r420855;
        double r420857 = t;
        double r420858 = r420857 + r420840;
        double r420859 = sqrt(r420858);
        double r420860 = sqrt(r420857);
        double r420861 = r420859 - r420860;
        double r420862 = r420856 + r420861;
        return r420862;
}