How many months jail did John Dean serve for his part in Watergate?

Although Dean was originally sentenced to 1-4 years in prison after he pled guilty, he ended up serving much less. Dean surrendered to the custody of the US Marshals on September 3, 1974, and was held in Fort Holabird, Maryland until January 8, 1975, when his sentenced was reduced to the time he had already served in custody -- just over 4 months.

Dean's lawyer moved to have his sentence reduced and on January 8, Judge Sirica granted the motion, adjusting Dean's sentence to time served, which wound up being four months. With his conviction for felony offenses, Dean was disbarred as a lawyer, so could no longer practice law.

https://en.wikipedia.org/wiki/John_Dean#Watergate_trial

Another reference:

While testifying before the Senate Watergate Committee in 1973, he implicated himself and other administration officials. Dean spent four months in prison and is now an active political commentator.

http://www.history.com/news/watergate-where-are-they-now