//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");