program main
	implicit none
	integer n
	integer i
	integer(8),allocatable,dimension(:)::c,d
	real(8)::total=0
	read(*,*)n
	allocate(c(n),d(n))
	do i=1,n
		read(*,*)c(i),d(i)
	enddo
	do i=1,n
		total=total+(c(i)/2)*d(i)
	enddo
	total=dmod(total,1000000007d0)
	write(*,*)nint(total)
end program main