9498.cpp

#include <iostream>

using namespace std;

int main()
{
	int score = 0;

	cin >> score;

	if (score >= 90)
		cout << "A" << endl;
	else if (score >= 80)
		cout << "B" << endl;
	else if (score >= 70)
		cout << "C" << endl;
	else if (score >= 60)
		cout << "D" << endl;
	else
		cout << "F" << endl;

	return 0;
}