P2857 [USACO06FEB] Steady Cow Assignment G

题目描述

Farmer John's N (1

输入格式

输出格式

说明/提示

Explanation of the sample: Each cow can be assigned to her first or second choice: barn 1 gets cows 1 and 5, barn 2 gets cow 2, barn 3 gets cow 4, and barn 4 gets cows 3 and 6.