//Do not declare variable marks.
//Write your code below this line.
if (marks > 90){
    console.log("AA");
}else if (90 <= marks > 80){
    console.log("AB");
}else if (80 <= marks > 70){
    console.log("BB");
}else if (70 <= marks > 60){
    console.log("BC");
}else if (60 <= marks > 50){
    console.log("CC");
}else if (50 <= marks > 40){
    console.log("CD");
}else if (40 <= marks > 30){
    console.log("DD");
}else if (marks > 30){
    console.log("FF");
}