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 r18971918 = x;
        double r18971919 = 1.0;
        double r18971920 = r18971918 + r18971919;
        double r18971921 = sqrt(r18971920);
        double r18971922 = sqrt(r18971918);
        double r18971923 = r18971921 - r18971922;
        double r18971924 = y;
        double r18971925 = r18971924 + r18971919;
        double r18971926 = sqrt(r18971925);
        double r18971927 = sqrt(r18971924);
        double r18971928 = r18971926 - r18971927;
        double r18971929 = r18971923 + r18971928;
        double r18971930 = z;
        double r18971931 = r18971930 + r18971919;
        double r18971932 = sqrt(r18971931);
        double r18971933 = sqrt(r18971930);
        double r18971934 = r18971932 - r18971933;
        double r18971935 = r18971929 + r18971934;
        double r18971936 = t;
        double r18971937 = r18971936 + r18971919;
        double r18971938 = sqrt(r18971937);
        double r18971939 = sqrt(r18971936);
        double r18971940 = r18971938 - r18971939;
        double r18971941 = r18971935 + r18971940;
        return r18971941;
}