Problem:
Score : 300 points

Problem Statement

Given are N integers A_1,\ldots,A_N.

Find the sum of A_i \times A_j over all pairs (i,j) such that 1\leq i < j \leq N, modulo (10^9+7).

Constraints

2 \leq N \leq 2\times 10^5

0 \leq A_i \leq 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
A_1 \ldots A_N

Output

Print \sum_{i=1}^{N-1}\sum_{j=i+1}^{N} A_i A_j, modulo (10^9+7).

Sample Input 1

3
1 2 3

Sample Output 1

11

We have 1 \times 2 + 1 \times 3 + 2 \times 3 = 11.

Sample Input 2

4
141421356 17320508 22360679 244949

Sample Output 2

437235829

Solution in Fortran (GNU Fortran 9.2.1) (judge verdict: Time Limit Exceeded)

program c177

implicit none
integer(16) :: n, ans, i, j
integer(16), allocatable :: a(:)

read *, n
allocate(a(1:n))

read*,  a(:)

ans = 0

do i = 1, n-1
 do j = i+1, n
  ans = ans + a(i) * a(j)
  !if(ans > 1000000007) then
   !ans = ans - 1000000007
  !end if
 end do
end do

print *, mod(ans,1000000007)

end program c177