Program to check whether a number is perfect or not

C      Program to check whether a number is perfect or not
        write(*,*)'Input the number:'
        read(*,*)n
        sum=0
        write(*,*)'The factors excluding that number are:'
        do i=1,(n/2)
        r=mod(n,i)
        if (r.eq.0)then
        write(*,*)i
        sum=sum+i
        end if
        end do
        if (sum .eq. n)then
        write(*,*)'The number is perfect.'
        else
        write(*,*)'The number is not perfect.'
        end if
        end