Sam's portfolio has two securities. The Pfizer stock has an expected return of 20% and a standard deviation of 23%. The Moderna stock has an expected return of 6% and a standard deviation of 11%. If the correlation between Pfizer and Moderna stocks is 

-1, what is the lowest possible standard deviation that Sam's portfolio can have? 

Answer in percentage points and include four decimal places; do not include the '%' in your answer, e.g., 10.1234 would be entered if the answer was 10.1234%. You do not need to input trailing zeros.