//Do not declare variable marks.
//Write your code below this line.
if(marks>90) 
    {console.log("AA");
    }
else if (90>=marks>80)
    {console.log("AB");
    }
else if(80>=marks>70)
       {console.log("BB");}
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{console.log("FF");}