HELP: Does anyone know why a piece of cardboard sticks to a glass of water when i turn it upside down?

Fill the drinking glass with water up to the brim.
Place the cardboard on top of the glass and hold it down. Some extra water may escape.
Hold the cardboard against the glass with your fingers and turn the glass over.
Carefully remove your fingers.
You should be surprised and amazed by this strange occurrence.
Repeat the experiment with a new piece of cardboard and only one inch of water in the glass.