def main():
    score = int(input(" 점수를 입력해주세요.:"))

    if score >= 90:
        grade = "A"
    elif score >= 80:
        grade = "B"
    elif score >= 70:
        grade = "C"
    elif score >= 60:
        grade = "D"
    else:
        grade = "F"

    print("당신의 성적은: "+grade + " 입니다.")

if __name__ == '__main__':
    main()