//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{
    console.log('FF')
}