#include <iostream>

using namespace std;

char courseGrade(int score);

int main()
{
    int testScore;

    cout << "Please input a test score : ";
    cin >> testScore;
    cout << courseGrade(testScore) >> endl;


    return 0;
}

char courseGrade(int score)
{
    switch (score / 10)
    {
    case 0:
    case 1:
    case 2:
    case 3:
    case 4:
    case 5:
        return 'F';
    case 6:
        return 'D';
    case 7:
        return 'C';
    case 8:
        return 'B';
    case 9:
    case 10:
        return 'A';
    }
}