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