//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
    console.log( "FF");