A cryptography problem:

Suppose that f: {0, 1}^m rightarrow {0, 1}^n is a preimage resistant bijective function. Define a hash function h: {0, 1}^2n rightarrow {0, 1}^n as follows. Given a bits string m Element {0, 1}^2n (of length 2n), write m = m_1 m_2 where m_1, m_2 Element {0, 1}^m. Then compute the message digest h (x) = f (m_1 m_2). Show that it is easy to solve Second Preimage problem for any m Element {0, 1}^2n