program main
        implicit none
        include 'mpif.h'

        integer i,j,ierr,myid,numprocs,x,status(MPI_STATUS_SIZE)
        integer destination,source,tag1,tag2

        call MPI_INIT(ierr)
        call MPI_COMM_SIZE(MPI_COMM_WORLD,numprocs,ierr)
        call MPI_COMM_RANK(MPI_COMM_WORLD,myid,ierr)

        tag1 = 7
        tag2 = 8

        do i=1,10
          if (mod(i,2) .eq. 0) then
            x = 0
            if (myid .lt. numprocs/2) then 
              destination = numprocs/2 + myid
              write(*,*) 'Sending from',myid
              call MPI_SEND(x,1,MPI_INTEGER,destination,tag1,
     1        MPI_COMM_WORLD,ierr)
            else 
              source = numprocs/2 - myid
              call MPI_RECV(x,1,MPI_INTEGER,source,tag1,MPI_COMM_WORLD,
     1        status,ierr)
              write(*,*) 'Received by',myid
            endif
          else
            x = 1
            if (myid .lt. numprocs/2) then 
              source = numprocs/2 + myid
              call MPI_RECV(x,1,MPI_INTEGER,source,tag2,MPI_COMM_WORLD,
     1        status,ierr)
            else 
              destination = numprocs/2 - myid
              call MPI_SEND(x,1,MPI_INTEGER,destination,tag2,
     1        MPI_COMM_WORLD,ierr)
            endif
          endif
        end do

        call MPI_FINALIZE(ierr)

        stop
        end