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