The girls of ballad duo 15& promised something amazing if they received ten thousand retweets.

"Did you enjoy our first stage?" Baek Ye Rin posted. "If this post gets RT'ed ten thousand times by tomorrow, producer J.Y. Park will come and perform "Somebody" with us at Gangnam Station! Please RT!"

"If this tweet gets RT'ed 10,000 times! We will perform with J.Y. Park tomorrow evening^^" Park Ji Min said.

Here are the tweets:�if you have a Twitter account, please go and share a retweet ... for science.