In 1930, Sténio Vincent, a long-time critic of the occupation, was elected President. By 1930, President Hoover had become concerned about the effects of the occupation, particularly after the December 1929 incident in Les Cayes. Hoover appointed a commission to study the situation, with William Cameron Forbes as the chair.:232-233 The Forbes Commission praised the material improvements that the U.S. administration had achieved, but it criticized the continued exclusion of Haitian nationals from positions of real authority in the government and the constabulary, which had come to be known as the Garde d'Haïti. In more general terms, the commission asserted that "the social forces that created  still remain - poverty, ignorance, and the lack of a tradition or desire for orderly free government." The Hoover administration did not fully implement the recommendations of the Forbes Commission; but United States withdrawal was under way by 1932, when Hoover lost the presidency to Franklin D. Roosevelt. The latter as Assistant Secretary of the Navy had overall responsibility for drafting the most recent Haitian constitution; he was a proponent of the "Good Neighbor policy" for the US role in the Caribbean and Latin America. On a visit to Cap-Haïtien in July 1934, Roosevelt reaffirmed an August 1933 disengagement agreement. The last contingent of U.S. Marines departed on August 15, 1934 after a formal transfer of authority to the Garde. The U.S. retained influence on Haiti's external finances until 1947.
Question: How many years did the U.S Marines retain influence on Haiti's external finances?
Answer: 13