#include <iostream>
#include <cstring>

using namespace std;

int main()
{
   int grade;
   string letter;
   cout<<"Enter your final score: ";
   cin>>grade;

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

   cout<<"Your letter grade = "<<letter<<endl;

   return 0;
}