sec1.4/milk3: copy it
sec1.4/milk3: copy it

Copy from http://www.programlife.net/usaco-mothers-milk-dfs.html

Signed-off-by: Kai Kang <a7030a8f1176a19bf7a462ae5dd59d92d5f9ca2f@gmail.com>

parr0tr1ver/usaco