
def binary_search(element, some_list, start_index=0, end_index=None):
    # end_index가 따로 주어지지 않은 경우에는 리스트의 마지막 인덱스
    if end_index == None:
        end_index = len(some_list) - 1
    if start_index > end_index:
        return None
    index = (start_index+end_index)//2
    if element == some_list[index]:
        return index
    elif element < some_list[index]:
        return binary_search(element,some_list, start_index, index-1)
    else:
        return binary_search(element,some_list, index+1, end_index)
    
    # 코드를 작성하세요.

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]))