P8660 [Lanqiao Cup 2017 National A] Interval Shifting

There are $n$ closed intervals on the number line: $D_1, \cdots ,D_n$. Interval $D_i$ is described by a pair of integers $[a_i,b_i]$, satisfying $a_i

The first line contains an integer $n$, indicating the number of intervals. The next $n$ lines each contain two integers $a_i,b_i$, separated by a space, representing the interval $[a_i,b_i]$. It is guaranteed that the sum of the lengths of the intervals is at least $10000$.

Output a number, representing the answer. If the answer is an integer, output only the integer part. If the answer is not an integer, round it to one decimal place.

**Sample Explanation** Sample 1: Move the first interval $10$ units to the left; move the second interval $20$ units to the right. Sample 2: Move the $2$-nd interval $0.5$ units to the right; move the $3$-rd interval $0.5$ units to the left. **Constraints** For $30\%$ of the test cases, $1 \le n \le 10$. For $100\%$ of the test cases, $1 \le n \le 10000$, $0 \le a_i