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