if(marks <=30){
    console.log("FF");
}else if(marks <=40 && marks >30){
        console.log("DD");

}else if(marks <=50 && marks >40){
        console.log("CD");

}else if(marks <=60 && marks >50){
        console.log("CC");

}else if(marks <=70 && marks >60){
        console.log("BC");

}else if(marks <=80 && marks >70){
        console.log("BB");

}else if(marks <=90 && marks >80){
        console.log("AB");

}else{
        console.log("AA");

}