//Do not declare variable marks.
//Write your code below this line.

if(marks>90)
    console.log("AA");
else
    if(marks>80)
        console.log("AB");
    else
        if(marks>70)
            console.log("BB");
        else
            if(marks>60)
                console.log("BC");
            else
                if(marks>50)
                    console.log("CC");
                   else
                       if(marks>40)
                            console.log("CD");
                        else
                            if(marks>30)
                                console.log("DD");
                            else
                                console.log("FF");