//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");