//Do not declare variable marks.
//Write your code below this line.
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 {
    console.log('FF');
}