//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'); 
}