#def index_equals_value_search(arr):
  #pass # your code goes here
#  for i in range(0,len(arr)):
#    if arr[i] == i:
#      return i

#  return -1


def binarySearch(arr,l,r):

    if l > r:
      return -1

    m = (l + r)/2
    currentIndex = -1

    if arr[m] == m:

      currentIndex = m
      binarySearch(arr,l,m-1)

    if arr[m] < m:
      return binarySearch(arr,m+1,r)

    if arr[m] > m:
      return binarySearch(arr,l,m-1)


    return currentIndex


def index_equals_value_search(arr):
  #pass # your code goes here
  # edge cases:
  if len(arr) == 0:
    return -1

  return binarySearch(arr,0,len(arr)-1)