The chance of coming up heads 99 times in a row is abysmally small: 50%^99 = 1.57 * 10^-30.
This however has already happened, it does not influence the next penny flip.
A penny has two sides, so the chance of it landing on one side is 1/2 = 0.5 = 50%.
So the result of the next flip has a chance of 50% of coming up heads.
