def binary_search(element, some_list, start_index = 0, end_index = None):
    if end_index == None:
        end_index = len(some_list) - 1

    # 코드를 작성하세요.
    if(start_index > end_index):
        return None
    mid_index = (start_index + end_index) // 2
    if(some_list[mid_index] == element):
        return mid_index
    elif(some_list[mid_index] > element):
        end_index = mid_index - 1
        return binary_search(element,some_list,start_index,end_index)
    else:
        start_index = mid_index + 1
        return binary_search(element, some_list, start_index, end_index)


print(binary_search(2, [2, 3, 5, 7, 11]))
print(binary_search(0, [2, 3, 5, 7, 11]))
print(binary_search(5, [2, 3, 5, 7, 11]))
print(binary_search(3, [2, 3, 5, 7, 11]))
print(binary_search(11, [2, 3, 5, 7, 11]))