#include <stdio.h>

int main() {
    int score = 0;
    scanf("%d", &score);
    if(score > 100)
    {
        printf("F");
    }
    else if(score >= 90)
    {
        printf("A");
    }
    else if(score >= 80)
    {
        printf("B");
    }
    else if(score >= 70)
    {
        printf("C");
    }else if(score >= 60)
    {
        printf("D");
    }
    else if(score >= 0)
    {
        printf("E");
    }
    else
    {
        printf("F");
    }
    return 0;
}
#include <stdio.h>

int main() {
    int score = 0;
    scanf("%d", &score);
    if(score >= 0)
    {
        switch (score / 10)
        {
            case 10:
            case 9:
                printf("A");
                break;
            case 8:
                printf("B");
                break;
            case 7:
                printf("C");
                break;
            case 6:
                printf("D");
                break;
            case 5:
            case 4:
            case 3:
            case 2:
            case 1:
            case 0:
                printf("E");
                break;
            default:
                printf("F");
                break;
        }
    }
    else 
    {
        printf("F");
    }

    return 0;
}