The PRI, or Institutional Revolutionary Party is one of the major lasting legacies of the Mexican Revolution; its first iteration was the Partido Nacional Revolucionario founded in 1929 under Northern revolutionary general and president of Mexico  Plutarco Elías Calles, following the assassination of president-elect  Álvaro Obregón in 1928. The establishment of the party created an enduring structure that managed not only presidential succession but also groups with competing interests. Initially, Calles remained the power behind the presidency during a period known as the Maximato, but his hand-picked presidential candidate, Lázaro Cárdenas, won a power struggle with Calles, expelling him from the country. Cárdenas reorganized the party that Calles founded, creating formal sectors for interest groups, including one for the Mexican military. The reorganized party was named Party of the Mexican Revolution.  In 1946, the party again changed its name to the Institutional Revolutionary Party. The party under its various names held the presidency from 1929 to 2000 and since 2012, is the party again in power.
Question: How many years after the assassination of Álvaro Obregón was the Partido Nacional Revolucionario founded?
Answer: 1