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