#include <iostream>

int main() {

        int students = 0;
        int grades = 0;
        int grades_sum = 0;
        int total_grade = 0;

        for ( int i = 1; i <= 30; i++  ) {

                std::cout << "Enter grade: ";
                std::cin >> grades;

                while ( grades < 0 || grades > 100 ) {

                        std::cout << "Error: invalid input. \n"
                                  << "Grades must be within "
                                  << "0 - 100."
                                  << std::endl;

                        std::cout << "Enter the grade again: ";
                        std::cin >> grades;

                }

                students++;
                grades_sum += grades;

        }

        std::cout << "The total number of grades entered: "
                  << students  << std::endl;

        return 0;
}