//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{
     console.log("FF"); 
}