https://www.acmicpc.net/problem/9498
#include <iostream>
#include <string>
using namespace std;
int main(){
int score;
cin >> score;
switch (score/10)
{
case 10:
case 9:
cout << 'A';
break;
case 8:
cout << 'B';
break;
case 7:
cout << 'C';
break;
case 6:
cout << 'D';
break;
default:
cout << 'F';
break;
}
return 0;
}