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