input: 
  from typing import List
  
  def count_pairs(numbers: List[int], x: int) -> int:
      """
      Count the number of pairs of integers in the list that sum up to the given value x.
      
      >>> count_pairs([2, 3, 5, 7, 11], 10)
      1
      >>> count_pairs([1, 9, 5, 0, 20, 15, 10], 20)
      3
      """
      count = 0
      i, j = 0, len(numbers) - 1
      while i < j:
          sum = numbers[i] + numbers[j]
          if sum == x:
              count += 1
              i += 1
          elif sum < x:
              i += 1
          else:
              j -= 1
      return count
  
output:     
      count = 0
      seen = set()
      for num in numbers:
          complement = x - num
          if complement in seen:
              count += 1
          seen.add(num)
      return count
  