Below is an instruction that describes a task. Write a response that appropriately completes the request in Chinese. Please answer in Chinese.

### Instruction:
 伊凡在他的院子里有一个鸟食盒，可以装两杯鸟食。每周，他都要重新装满空的鸟食盒。每杯鸟食可以喂养十四只鸟，但伊凡经常赶走一只偷走半杯鸟食的饥饿松鼠。伊凡的鸟食盒每周可以喂养多少只鸟？


### Response:
 每周松鼠偷走1/2杯鸟食，所以鸟吃掉了2 - 1/2 = 1 1/2杯鸟食。
每杯鸟食可以喂养14只鸟，所以伊凡的鸟食盒每周可以喂养14 * 1 1/2 = 21只鸟。