//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.lof("BB");
}else if(70 >= marks < 60) {
    console.lof("BC");
}else if(60 >= marks < 50) {
    console.lof("CC");
}else if(50 >= marks < 40) {
    console.lof("CD");
}else if(40 >= marks < 30) {
    console.lof("DD");
}else {
    console.lof("FF");
}