Three friends worked in the same office & shared a flat on the 110th floor of a New York City high rise apartment building.
One day they returned from their office to discover that the lift was not working. So they decided to climb the stairs to their 110th floor.
To pass the time & not get bored they agreed to tell some story.
The 1st person was tell a story about a war, the 2nd person a romance story & the 3rd person a very sad story.
The first person told a story about the US & Vietnam War which lasted till they reached 50th floor.
The Second person completed his romance story by the time they reached 109th floor.
Now was the turn of the third person to tell a very sad story . . .
. . .And his story was "I forgot to bring the Key to the flat".