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