114. Telecasting station
time limit per test: 0.25 sec.
memory limit per test: 4096 KB
Every city in Berland is situated on Ox axis. The government of the country decided to build new telecasting station. After many experiments Berland scientists came to a conclusion that in any city citizensdispleasure is equal to
product of citizens amount in it by distance between city and TV-station. Find such point on Ox axis for station so that sum ofdispleasures of all cities is minimal.
Input
Input begins from line with integer positive number N (0<N<15000) – amount of cities in Berland. FollowingN pairs
(X, P) describes cities (0<X, P<50000), whereX is a coordinate of city and
P is an amount of citizens. All numbers separated by whitespace(s).
Output
Write the best position for TV-station with accuracy 10-5.
Sample Input
4
1 3
2 1
5 2
6 2
Sample Output
3.00000
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