#include <stdio.h>
int main() {
    float grade;
    scanf("%d", &grade);
if(grade>=90 && grade<=100){
    printf("A");
   }
   else if (grade>=80 && grade<=89){
   printf("B");}
   else if (grade>=70 && grade<=79){
   printf("C");}
   else if (grade>=60 && grade<=69){
   printf("D");}
   else
    printf("FAIL");
return 0;
}