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