//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");