"""Compute the letter grade given a numeric score"""

def letter_grade(score) :

    if score < 60 :
        grade = 'F'
    else :
        if score < 70 :
            grade = 'D'
        else :
            if score < 80 :
                grade = 'C'
            else :
                if score < 90 :
                    grade = 'B'
                else :
                    grade = 'A'

    return grade

if __name__ == '__main__' :
    score = input("enter score: ")
    grade = letter_grade(score)
    print "the letter grade is:", grade