double grade_aux(const Student_info& s)
{
	try {
		return grade(s);
	} catch (domain_error) {
		return grade(s.midterm, s.final, 0);
	}
}

// this version works fine
double median_analysis(const vector<Student_info>& students)
{
	vector<double> grades;

	transform(students.begin(), students.end(),
	          back_inserter(grades), grade_aux);
	return median(grades);
}