//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");