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=[int(x) for x in input().split()]
  m=10**9+7
  s=0
  for c in range(n):
      s=(s+a[c])%m
  s=pow(s,2,m)
  for c in range(n):
      s=(s-pow(a[c],2,m))%m
  if s%2==0:
      print(s//2)
  else:
      print((s+m)//2)
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"}]