The AFL was growing rapidly, from 2.1 million members in 1933 to 3.4 million in 1936. But it was experiencing severe internal stresses regarding how to organize new members. Traditionally, the AFL organized unions by craft rather than industry, where electricians or stationary engineers would form their own skill-oriented unions, rather than join a large automobile-making union. Most AFL leaders, including president William Green, were reluctant to shift from the organization's longstanding craft unionism and started to clash with other leaders within the organization, such as John L. Lewis. The issue came up at the annual AFL convention in San Francisco in 1934 and 1935, but the majority voted against a shift to industrial unionism both years. After the defeat at the 1935 convention, nine leaders from the industrial faction led by Lewis met and organized the Committee for Industrial Organization within the AFL to "encourage and promote organization of workers in the mass production industries" for "educational and advisory" functions. The CIO, which later changed its name to the Congress of Industrial Organizations , formed unions with the hope of bringing them into the AFL, but the AFL refused to extend full membership privileges to CIO unions. In 1938, the AFL expelled the CIO and its million members, and they formed a rival federation. The two federations fought it out for membership; while both supported Roosevelt and the New Deal, the CIO was further to the left, while the AFL had close ties to the big city machines.
Question: How many years after the 2nd convention in San Francisco where the majority voted against a shirt to industrial unionism did the AFL expell the CIO and formed a rival federation?
Answer: 3