program greetings_comm
    implicit none
    include 'mpif.h'
    integer :: my_rank, np, sender, recipient, tag, ln, ierr
    integer :: status(MPI_STATUS_SIZE)
    character(100) :: message=", greetings from "
    character(100) :: name=" "

   call MPI_Init(ierr)
   call MPI_Comm_rank(MPI_COMM_WORLD, my_rank, ierr)
   call MPI_Comm_size(MPI_COMM_WORLD, np, ierr)

   sender = my_rank - 1;  recipient = my_rank + 1
   if ( my_rank == 0 ) then
      write(6,FMT="(A)") "What's your name?"
      read(5,"(A)") name
      ln = len_trim(name)
   endif
   
   if ( sender >= 0 ) then
      tag = 0
      call MPI_Recv(ln, 1, MPI_INTEGER, sender, tag, MPI_COMM_WORLD, status, ierr)
      tag = 1
      call MPI_Recv(name, ln, MPI_CHARACTER, sender, tag, MPI_COMM_WORLD, status, ierr)
   endif
   
   if ( recipient < np ) then
      tag = 0
      call MPI_Send(ln, 1, MPI_INTEGER, recipient, tag, MPI_COMM_WORLD, ierr)
      tag = 1
      call MPI_Send(name, ln, MPI_CHARACTER, recipient, tag, MPI_COMM_WORLD, ierr)
   endif   
   
   write(6,FMT="(3A,I3)") "Hi ",TRIM(name),TRIM(message),my_rank
   
   call MPI_Finalize(ierr)
end program greetings_comm