program calcolamedia
implicit none
integer ::i,n,iend
real :: x,y,s,media

n=0
s=0
do i=1,10000000
   read(5,*,iostat=iend)x,y
   if(iend /=0) then
      exit
   endif

   s=s+x
   n=n+1
!   write(6,*)n,x,s
enddo
if (iend >0)then
   write(6,*) 'errore lettura'
else
   media=s/n
   write(6,*)media
endif
end program calcolamedia