[Usaco2016 Dec]Cities and States

时间限制：10s 空间限制：128MB

To keep his cows intellectually stimulated, Farmer John has placed a large map of the USA on the wal

l of his barn. Since the cows spend many hours in the barn staring at this map, they start to notice

several curious patterns. For example, the cities of Flint, MI and Miami, FL share a very special r

elationship: the first two letters of "Flint" give the state code ("FL") for Miami, and the first tw

o letters of "Miami" give the state code ("MI") for Flint.Let us say that two cities are a "special

pair" if they satisfy this property and come from different states. The cows are wondering how many

special pairs of cities exist. Please help them solve this amusing geographical puzzle!

The first line of input contains N (1≤N≤200,000), the number of cities on the map.The next N lines

each contain two strings: the name of a city (a string of at least 2 and at most 10 uppercase lette

rs), and its two-letter state code (a string of 2 uppercase letters). Note that the state code may b

e something like ZQ, which is not an actual USA state. Multiple cities with the same name can exist,

but they will be in different states.

依次给出N（1≤N≤200,000）个城市名及其州的代码（州代码保证仅有两位）。我们说，两个城市是一个“特殊对

”，如果他们来自不同的州且A城市的州代码是B城市的城市名首两位，B城市的州代码是A城市的城市名首两位。问

：在给定的信息中有多少个“特殊对”？

Please output the number of special pairs of cities.

6
MIAMI FL
DALLAS TX
FLINT MI
CLEMSON SC
BOSTON MA
ORLANDO FL