program exercise

 implicit none

 integer              :: n,np,i,k
 real*8,  allocatable :: a(:)
 integer, allocatable :: tmp(:)
 real*8               :: even,odd

 !1)
 do 
  write(*,*) 'Array size (>1)'
  read(*,*) n
  if (n.gt.1) exit
 enddo 
  
 allocate(a(n))

 write(*,*) 'Array'
 read(*,*) a


 !2)
 even=0.d0
 do i=2,n,2
    even=even+a(i)
 enddo   

 odd=0.d0
 do i=1,n,2
    odd=odd+a(i)
 enddo   

 write(*,*) 'Value of even', even
 write(*,*) 'Value of odd', odd
 !3)
 np=n/2
 if (even.gt.odd) then
    allocate(tmp(np))
    k=0
    do i=2,n,2
       k=k+1
       tmp(k)=int(a(i))
    enddo   
    call bubblep(tmp,np)
 else
    if (mod(n,2).ne.0) np=np+1
    allocate(tmp(np))
    k=0
    do i=1,n,2
       k=k+1
       tmp(k)=int(a(i))
    enddo   
    call bubblem(tmp,np)
 endif

 !4)
 open(10,file='out.dat')

 do i=1,np
    write(10,100) i,tmp(i)
 enddo 

 close(10)

 deallocate(a)
 deallocate(tmp)

100 format(2(I4))

 stop

end program exercise


subroutine bubblep(x,n)

 implicit none

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

 integer                 :: i,j


 do i=1,n
    do j=2,n-(i-1)
       if (x(j-1).gt.x(j)) then
          call swap(x(j-1),x(j))
       endif
    enddo
 enddo

 return

end subroutine bubblep

subroutine bubblem(x,n)

 implicit none

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

 integer                 :: i,j
     

 do i=1,n
    do j=2,n-(i-1)
       if (x(j-1).lt.x(j)) then
          call swap(x(j-1),x(j))
       endif
    enddo
 enddo

 return

end subroutine bubblem

subroutine swap(x,y)

 implicit none

 integer, intent(inout)    :: x,y

 integer                   :: tmp

 tmp=x
 x=y
 y=tmp

 return

end subroutine swap