What I heard in my younger days is modified and retold here….
Two countries were in a constant conflict and cold war.... Each was worried about an attack by the other at any time.... In their own safety, each had formulated a number of Innovative Security Policies to guard them against spying and other indirect attacks.... Thus, each had excelled the other in many security and safety measures.... And at the back of this elaborate security background, the life was going on….
On one occasion, the Secret Agent of one country had to visit the other to deliver some important data physically to another Agent of their own operating in that country.... He had one week Crash Course Training at his Head Quarters on the ways he had to behave in the enemy area, prove himself as the right person with their own men positioned there as Secret Agents and get through his work….
He had an elaborate plan in front of him and was briefed on all the steps he had to take to identify himself there in the right manner.... He was given a week time to go, complete his job and be back.... The Agent followed all the steps diligently and soon entered the other country secretly at mid night through the innovative methods he was taught.... He could thus move ahead, sneaked into the city and further to the right address and entered a multi storied Housing Complex....
He went up to the required floor level and knocked at the door of the flat required three times simultaneously making a scratching sound on the door instead of pressing the Calling Bell as a first measure of getting himself identified in the right way as taught….
A man opened the door….
The Agent smiled at him, showed his palm with middle finger at the centre of it and said, "The sky is clear, the moon may rise shortly but the darkness is reigning this moment and I am on a difficult job.... Just now, the wind has started blowing but still the twinkling of stars is seen so clearly with no signs of any rain coming up..... Can I get some water to drink and relax till my way is through?”
The man looked at him and said, “Oh! You wanted the man living above us..... His Flat is exactly above ours.... His Floor is 12A and you are at 12 Level ...You got confused between 12 and 12A as in our country we don't have 13 at many places!”