Here is the English translation:
Problem Description
Given ( n ) points ((x_i, y_i)) on the plane, define [ d(i,j)=\sqrt{(x_i - x_j)^2 + (y_i - y_j)^2}. ] Compute [ \sum_{1 \le i < j \le n} d(i,j). ]
Input Format
The first line of the input contains an integer ( n ).
The next ( n ) lines each contain two integers ( x_i, y_i ).
Output Format
Output a single real number — the answer. The absolute error must not exceed (10^{-4}).
Sample Data
Sample Input
3
1 2
-1 3
0 -1Sample Output
9.5214512632858295782294770691381Sample Explanation
The answer is ( d(1,2) + d(1,3) + d(2,3) = \sqrt{5} + \sqrt{10} + \sqrt{17} ).
Subtasks
For all test cases: (1 \le n \le 5 \times 10^5), ( -10^6 \le x_i, y_i \le 10^6).
- Subtask 1 (10 points): ( n \le 3{,}000 )
- Subtask 2 (20 points): ( n \le 40{,}000 )
- Subtask 3 (30 points): ( n \le 10^5 )
- Subtask 4 (20 points): ( n \le 3 \times 10^5 )
- Subtask 5 (20 points): No additional constraints.