#include <iostream>

using namespace std;

int main()
{
  int grade;
  cout << "Enter the student's numerical grade: ";
  cin >> grade;

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

}