President Donald Trump said he doesn’t have to “prepare very much” for his June 12 summit with North Korean leader Kim Jong Un, saying success in the meeting will be “about attitude.”

“I think I’m very well prepared,” Trump told reporters Thursday during a meeting at the White House with Japanese Prime Minister Shinzo Abe. “I don’t think I have to prepare very much. It’s about attitude, it’s about willingness to get things done.”

“This isn’t a question of preparation: It’s a question of whether or not people want it to happen, and we’ll know that very quickly,” Trump continued. Trump added both he and Kim have been preparing “for a long time.”

Trump predicted a “very fruitful meeting” with Kim in Singapore next week and left open the possibility it could continue for several sessions. Asked how many days the summit would last, Trump responded, “One, two, three, depending on what happens.”

Secretary of State Mike Pompeo, who has traveled to Pyongyang twice since March, has prepared Trump for the summit in about eight-to-ten hours of briefings per week for several weeks, two U.S. officials said. The CIA’s top Korea expert, Andrew Kim, has also helped with the Trump briefings.

On Tuesday, former senators Sam Nunn and Richard Lugar briefed Trump and Vice President Mike Pence on their lessons learned co-sponsoring a law aimed at securing and dismantling nuclear weapons after the fall of the Soviet Union.