Tugas JAVA NETBEANS

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;


    BufferedReader nilai = new BufferedReader(new InputStreamReader(System.in));
    try{
        System.out.println("Masukan nilai anda :");
        int n =Integer.parseInt(a.readLine());
        if (n>=81)System.out.println("Nilai anda A");
        else if(n>=71) System.out.println("Nilai anda B");
        else if(n>=51) System.out.println("Nilai anda C");
        else if(n>=41) System.out.println("Nilai anda D");
}catch(IOException e ){
System.out.println("error!");

}
    }
  
}