output_description: Print \sum_{i=1}^{N-1}\sum_{j=i+1}^{N} A_i A_j, modulo (10^9+7).
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
      A_1 \ldots A_N
attempt: N = int(input())
  A_list = list(map(int, input().split()))
  # myans_list =  [ [0 for n in range(N)] for nn in range(N) ]
  # myans = 0
  # for n in range(N):
  #    for nn in range(N):
  #        myans_list[n][nn] = A_list[n] * A_list[nn]
  # for n in myans_list:
  #    print(n)
  mysum = sum(A_list)
  myans = 0
  for n in range(N - 1):
      mysum -= A_list[n]
      myans += mysum * A_list[n]
  print(myans % (1000000007))
  
problem_description: 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).
samples: [{"input": "3\n    1 2 3", "output": "11\n    \n\nWe have 1 \\times 2 + 1 \\times 3 + 2 \\times 3 = 11.\n\n* * *"}, {"input": "4\n    141421356 17320508 22360679 244949", "output": "437235829"}]