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

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