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