program main

 implicit none

 integer              :: ii,i,n,nc,sa,j
 integer, allocatable :: a(:),b(:)
 real*8,  allocatable :: c(:,:)
 character*20         :: input

!1)
 write(*,*) 'Name of input file'
 read(*,*) input

 open(10,file=input)
 read(10,*) n
 allocate(a(n))
 do i=1,n
    read(10,*) a(i)
 enddo   
 close(10)

!2)
 if (mod(n,2).eq.0) then
    nc=n/2
 else   
    nc=n/2+1
 endif   
 allocate(b(nc))
 ii=0
 do i=1,n,2
    ii=ii+1
    b(ii)=a(i)
 enddo 
 call bubble (b,nc)
 sa=0
 do i=2,n,2
    sa=sa+a(i)
 enddo   
 write(*,*) 'Sum is', sa

!3) 
 allocate(c(n,n))
 if (sa.gt.0) then
    do i=1,n
       do j=1,n
          c(i,j)=a(i)+i**2
       enddo   
    enddo   
 else   
    do i=1,n
       c(i,i)=a(i)
    enddo 
    do i=1,n
       do j=i+1,n
          c(i,j)=dble(sa)/dble(i+j)
          c(j,i)=c(i,j)
       enddo   
    enddo   
 endif

!4)

 open(11,file='b.dat')
 open(12,file='c.dat')

 do i=1,nc
    write(11,100) i, b(i)
 enddo   

 do i=1,n
    do j=1,n
       write(12,101) i,j,c(i,j)
    enddo   
 enddo 

 close(11)
 close(12)

100 format(2(I5))
101 format(2(I5),F10.5)

 stop
end program main


subroutine bubble(c,n)

 implicit none

 integer, intent(in) :: n
 integer, intent(inout) :: c(n) 

 integer  :: i,j 

 do i=1,n
    do j=n,i+1,-1
       if (c(j-1).lt.c(j)) then
          call swap(c(j-1),c(j))
       endif
    enddo
 enddo 

 return

end subroutine bubble 


subroutine swap(x,y)

 implicit none

 integer, intent(inout)    :: x,y
 integer                   :: tmp

 tmp=x
 x=y
 y=tmp

 return

end subroutine swap