//Do not declare variable marks.
//Write your code below this line.
var result = 'FF';

if(marks > 90){
    result = 'AA';
}
else if (marks > 80 && marks <= 90){
    result = 'AB';
}
else if (marks > 70 && marks <= 80){
    result = 'BB';
}
else if (marks > 60 && marks <= 70){
    result = 'BC';
}
else if (marks > 50 && marks <= 60){
    result = 'CC';
}
else if (marks > 40 && marks <= 50){
    result = 'CD';
}
else if (marks > 30 && marks <= 40){
    result = 'DD';
}

console.log(result);