#include <iostream>

using namespace std;

int main()
{
	int mark;
	char grade;

	cout << "Enter your mark: ";
	cin >> mark;
  
	if (mark >= 80)
		grade = 'A';
	else if (mark >= 70)
		grade = 'B';
	else if (mark >= 60)
		grade = 'C';
	else if (mark >= 50)
		grade = 'D';
	else
		grade = 'F';

	cout << "Your grade is " << grade << endl;

	return 0;
}