Nomor 2 if else stringbuffer

package tugasbuffer;
import java.io.*;


/**
 *
 * @author kalvin jr
 */
public class Tugasbuffer {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String nama,stb,almt,grade,ket;
        int nt,nm,nf;
        double na;
       try {
        System.out.print("Masukkan Stambuk Anda : ");
        stb = br.readLine();
        System.out.print("Masukkan Nama :");
        nama = br.readLine();
        System.out.print("Masukkan Alamat :");
        almt = br.readLine();
        System.out.print("Masukkan Nilai Tugas :");
        nt =Integer.parseInt(br.readLine());
        System.out.print("Masukkan Nilai Mid : ");
        nm =Integer.parseInt(br.readLine());
        System.out.print("Masukkan Nilai Final : ");
        nf=Integer.parseInt(br.readLine());

        na =((nt*0.3)+(nm*0.3)+(nf*0.4));

        if((na>=80) && (na<=100)){
             grade = "A";
             ket ="Sangat Baik";
         }
         else if((na>=65) && (na < 80)){
             grade = "B";
             ket = "Baik";
         }
         else if((na>=50)&&(na<65) ){
             grade = "C";
             ket = "Kurang";
         }
         else if((na>=35) && (na <50 )){
             grade = "D";
             ket = "Sangat Kurang";
         }
         else {
        grade = "E";
        ket = "Eror";
        }
        System.out.println("STAMBUK : "+stb);
        System.out.println("NAMA : "+nama);
        System.out.println("ALAMAT : "+almt);
        System.out.println("NILAI TUGAS :"+nt);
        System.out.println("NILAI MID :"+nm);
        System.out.println("NILAI FINAL : "+nf);
        System.out.println("NILAI AKHIR :"+na);
        System.out.println("NILAI HURUF : "+grade);
        System.out.println("KETERANGAN : "+ket);


       }catch (IOException e){
           System.out.print("Eror"+e.getMessage());
       }


        // TODO code application logic here
    }

}