Send a text to Luka Urushibara’s pager six days in the past with the winning numbers for the third-place lottery prize (six numbers total).
The world changes instantly. In this new worldline, the lottery experiment never happened, and Daru has no memory of sending the text. However, Okabe finds a scrap of paper in Luka's pocket showing that while Luka did receive the numbers, Okabe’s own poor handwriting caused Luka to buy the wrong ticket. The Warning from John Titor Steins;Gate (Dub) Episode 7
Titor claims that if Okabe can change the world's "divergence" by more than 1%, he can reach the Steins Gate worldline where the dystopia is averted. Send a text to Luka Urushibara’s pager six