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