program mpi2

      include 'mpif.h'

      integer nproc, ich, i, N, ier
      real    sum, Gsum

      call MPI_Init(ier)
      call MPI_Comm_size(MPI_COMM_WORLD, nproc, ier)
      call MPI_Comm_rank(MPI_COMM_WORLD, ich, ier)

      if (ich .eq. 0) then
        write(*,100) 
100     format('*** Geben Sie bitte die Anzahl Terme ein: N = ',$)
        read(*,*) N
      end if
      call MPI_Bcast(N,1,MPI_INTEGER,0,MPI_COMM_WORLD,ier)

      sum=0.
      do i=ich,N-1,nproc
        if (mod(i,2).eq.0) then
          sum = sum + 1. / real(i + 1)
        else
          sum = sum - 1. / real(i + 1)
        end if
      end do
      call MPI_Reduce(sum,Gsum,1,MPI_REAL,MPI_SUM,0,MPI_COMM_WORLD,ier)
      if (ich .eq. 0) write(*,200) Gsum
200   format('*** Eine Schaetzung von ln(2) ist ',f12.6)

      call MPI_Finalize(ier)
      end