Smile on Milk Carton

Every night, the little girl puts a carton of milk on the windowsill, waiting for her father who works overtime. On her birthday night, she put down the milk and fell asleep as usual. In the early morning, my father came back, drank the milk, and drew a smiley face on the box. The next day, she smiled when she saw the empty box and the smiling face - expecting to be late sometimes, but never absent.