input: Write a python function to calculate the average score of each student in a dictionary.
  assert average_scores({'John': {'Math': 91, 'English': 83}, 'Mary': {'Math': 94, 'English': 93}}) == {'John': 87.0, 'Mary': 93.5}
  assert average_scores({'Alice': {'Math': 88, 'English': 92}, 'Bob': {'Math': 75, 'English': 85}}) == {'Alice': 90.0, 'Bob': 80.0}
  assert average_scores({'Charlie': {'Math': 100, 'English': 100}, 'David': {'Math': 60, 'English': 70}}) == {'Charlie': 100.0, 'David': 65.0}
output: def average_scores(students):
      result = {}
      for student, scores in students.items():
          average = sum(scores.values()) / len(scores)
          result[student] = average
      return result