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  1. n=int(input())
  2. A=list(map(int, input().split()))
  3. target=int(input())
  4. counter=0
  5. mp={}
  6. for j in range(n):
  7. r=target + A[j]
  8. counter+=mp.get(r, 0)
  9. mp[A[j]]=mp.get(A[j], 0) + 1
  10. print(counter)
Success #stdin #stdout 0.09s 14172KB
stdin
5
10 5 7 3 8
2
stdout
2