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

var o;
if (marks > 90) {
    o = "AA";
} else if (marks > 80) {
    o = "AB";
} else if (marks > 70) {
    o = "BB";
} else if (marks > 60) {
    o = "BC";
} else if (marks > 50) {
    o = "CC";
} else if (marks > 40) {
    o = "CD";
} else if (marks > 30) {
    o = "DD";
} else {
    o = "FF";
}

console.log(o);