double dichotomy(double infinum, double supremum, double epsilon) {
   double x;
   while (supremum - infinum > epsilon) {
      x = (infinum + supremum) / 2;
      if (func(supremum) * func(x) < 0)
         infinum = x;
      else
         supremum = x;
   }
   return (infinum + supremum) / 2;
}