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