//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 if (marks <= 30){
    console.log('FF');
}