Getting the intergalactic message across is easier said than done

"Scientists recently decoded the first confirmed alien transmission from outer space. It said:

'Please send 5x10 (to the 50th power) atoms of hydrogen to each of the five star systems listed below. Then, add your system to the top of the list and delete the system at the bottom. Transmit copies of this message to 100 different solar systems. If you follow these instructions, you are guaranteed that within 0.25 degrees of a galactic rotation you will receive in return sufficient hydrogen stores to power your own civilization until the universe reaches inevitable maximum entropy. This really works!'"

This is from a quite interesting piece on the present state of SETI (the Search for Extraterrestrial Intelligence). I'm collecting my hydrogen atoms now.