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