//Do not declare variable marks.
//Write your code below this line.
if(marks>90)
    console.log("AA");
else if(marks <=90 || marks >80)
    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");