How do you beat level 15 on 40x Escape

Press just the S and then the P.
The puzzle changes the color of the letter that you press and of the letters adjacent to it. (on to off or off to on). The goal is to turn all the letters on, so with six letters in "escape" you only need to press the middle letter in the first set of three (the S) and the middle letter in the second set of three (the P).