text: #include <stdio.h>
  
  int main(){
      int n;
      scanf("%d", &n);
  
      switch (n){
          case 90 ... 100:
              printf("A");
              break;
          case 80 ... 89:
              printf("B");
              break;
          case 70 ... 79:
              printf("C");
              break;
          case 60 ... 69:
              printf("D");
              break;
          case 0 ... 59:
              printf("F");
              break;
          default:
              printf("Error");
              break;
      }
  
      return 0;
  }
  