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114. Telecasting station time limit per test: 0.25 sec.
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 citizens displeasure 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 of displeasures of all cities is minimal.
Input Input begins from line with integer positive number N (0<N<15000) – amount of cities in Berland. Following N pairs (X, P) describes cities (0<X, P<50000), where X 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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