You have invested a total of $1 million in your venture and you target to achieve a minimum value of $10 million for your shares in the venture at the point of exit, which is at the end of Year 5. However, you estimate that your venture would require two rounds of external funding of $4 million at the end of Year 2 and $2 million at the end of Year 3, at pre-money valuation of $x million and $15 million respectively. If the estimated total equity value of your venture at the point of exit is $50 million, what minimum pre-money valuation must the first external round of funding be (what is the minimum value of x)?