## SGU 114 解题报告

http://acm.sgu.ru/problem.php?contest=0&problem=114

## 114. Telecasting station

time limit per test: 0.50 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 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.

4
1 3
2 1
5 2
6 2

### Sample Output

3.00000

sigma(wi)(xi < xk) <= W/2

sigma(wi)(xi > xk) <= W/2

### CODE

#include
#include
#include
using namespace std;
struct node
{
double x;
long long p;
}D[15005];
bool cmp(node a,node b)
{
return (a.x=mid) break;
}
printf("%.5lfn",D[i].x);
return 0;
}