in february 2008, harvard graduate and technical architect nathan blecharczyk became the third co-founder of airbnb. each co-founder assumed a role within the new company, with chesky becoming the leader and chief executive officer. in order to receive funding, chesky and his co-founders created special-edition cereals called "obama o’s" and "cap'n mccains", based onn presidential candidates barack obama and john mccain. impressed by the cereal boxes, y combinator accepted airbnb into its seed funding program. in its first year, the company began internationalizing and opened several offices in europe. in 2011, chesky wrote a letter on behalf of the company for its handling of a resident complaint about tenant vandalism by announcing a 24-hour hotline, additional staff support and a guarantee for theft or vandalism. in 2015, chesky announced that airbnb was an official sponsor of the 2016 summer olympics in rio de janeiro, brazil. he said that more than 120,000 people had stayed in airbnb homes during the 2014 fifa world cup. as of march 2015, airbnb has a $20 billion valuation.