Can someone tell me what is wrong with the code I am writing? I am trying to find a sum of all elements in this list. My code:

```py
def determine_sum(m_list, sum_count): 

    for i in range(len(m_list)): 

        if isinstance(m_list[i], int):      
            sum_count += m_list[i]  

        else:  
            return determine_sum(m_list[i], sum_count)

    return sum_count 

m_list = [1, 2, 3, [4, 5], [4, [3,4]] ]

print(determine_sum(m_list, 0))

```

The output is `15`, but I expected `26`.