//Do not declare variable marks.
//Write your code below this line.
marks = parseInt(marks, 10);
if (marks > 90) {
    console.log('AA');
} else if (marks > 80 && marsk <= 90) {
    console.log('AB');
} else if (marks > 70 && marsk <= 80) {
    console.log('BB');
} else if (marks > 60 && marsk <= 70) {
    console.log('BC');
} else if (marks > 50 && marsk <= 60) {
    console.log('CC');
} else if (marks > 40 && marsk <= 50) {
    console.log('CD');
} else if (marks > 30 && marsk <= 40) {
    console.log('DD');
} else if (marks <= 30) {
    console.log('FF');
}