SAP智力題 Bird shit III ★★★★★★★★

When a group of guys were walking, some birds flew over and left shits on their heads. Everyone can see shits on other guys' heads, but cannot see that on his own head. They entered a coffee shop, the seller said: “There are 3 guys among you who have same count of shits, and there are a few pairs, the guys within each pair have same count, the rest have different count of shits. Of course, the counts for all the pairs and previous mentioned 3 guys are all different. You guys must not communicate. If anyone can make a correct guess of his own count, I will provide free coffee to all of you.” If the guys could imagine the situation and could have a discussion before hand, they are sure to find a stategy. Do you known how many guys there are at most? http://forums.sdn.sap.com/thread.jspa?threadID=1852017&tstart=0