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