// Java program that illustrates nested function calls.
public class abcd
{
  public static void main(String [] args)
  {
    a();
    System.out.println();
    b();
    System.out.println();
    c();
    System.out.println();
    d();
    System.out.println();
  }

  public static void a()
  {
    System.out.print("a");
  }

  public static void b()
  {
    a();
    System.out.print("b");
  }

  public static void c()
  {
    a();
    b();
    System.out.print("c");
  }

  public static void d()
  {
    a();
    b();
    c();
    System.out.print("d");
  }
}

////////////////////////////////////////////
// The output of the program is:
// a
// ab
// aabc
// aabaabcd
////////////////////////////////////////////