The von Neumann extractor uses two input bits to produce either zero or one output bits, so the output is shorter than the input by a factor of at least 2. On average the computation discards proportion "p"2 + (1 − "p")2 of the input pairs(00 and 11), which is near one when "p" is near zero or one, and is minimized at 1/4 when "p" = 1/2 for the original process (in which case the output stream is 1/4 the length of the input stream on average).