input: def count_pairs(numbers: List[int], x: int) -> int:
      """
      Generate a Python program to count the number of pairs with a given sum x in a list of numbers.
      
      >>> count_pairs([1, 4, 2, 3, 6, 5], 10)
      1
      >>> count_pairs([1, 5, 3, 7, 6, 4], 10)
      2
      """
output:     count = 0
      seen = set()
      for num in numbers:
          complement = x - num
          if complement in seen:
              count += 1
          seen.add(num)
      return count