program sommatoria
implicit none
integer:: i,n,somma

! versione con do while

do while(.true.)
   write(6,*)'dammi N positivo'
   read(5,*) n
   
   if(n < 0) then
      write(6,*)'Ho detto positivo !!!!'
   else
      somma=0
      i=1
      do while(i <= n)
         somma=somma+i
         i=i+1
      enddo
      write(6,*)'somma=',somma
   endif
enddo
end program sommatoria