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 if(marks<=30)console.log("FF");