#include <iostream>
#include <limits>

using namespace std;
 
int main()
{
	cout << "Digite uma letra (A-F): " << endl;

	
	char grade;
	
	while ((grade = cin.get()) != EOF)
	{
		cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
		switch ( grade )
        {
        	case 'A':
            case 'a':
               cout << "A" << endl;
               break;
            case 'B':
            case 'b':
               cout << "B" << endl;
               break;
            case 'C':
            case 'c':
               cout << "C" << endl;
               break;
            case 'D':
            case 'd':
               cout << "D" << endl;
               break;
            case 'F':
            case 'f':
               cout << "F" << endl;
               break;
            default:
               cout << "Incorrect letter grade entered." << " Enter a new grade." << endl;
               break;
    }
		
	}
}