Input
The first line contains a single integer , the number of points on a plane.
Each of the next
lines contains two real coordinates
the
th point specified with exactly 2 fractional digits.
Output
Output a real number representing the answer. The absolute or relative error of your answer should be at most .
Constraints
Example 1
Input
8
-2.14 2.06
-1.14 2.04
-2.16 1.46
-2.14 0.70
-1.42 0.40
-0.94 -0.48
-1.42 -1.28
-2.16 -1.62
5.410
Example 2
Input
5
2.26 1.44
2.28 0.64
2.30 -0.30
1.58 0.66
3.24 0.66
5.620
Example 3
Input
8
6.98 2.06
6.40 1.12
5.98 0.24
5.54 -0.60
7.16 0.30
7.82 1.24
8.34 0.24
8.74 -0.76
5.480
Example 4
Input
5
10.44 2.06
10.90 0.80
11.48 -0.48
12.06 0.76
12.54 2.06
6.040
Example 5
Input
8
16.94 2.42
15.72 2.38
14.82 1.58
14.88 0.50
15.76 -0.16
16.86 -0.20
17.00 0.88
16.40 0.92
6.040
Example 6
Input
7
20.62 3.00
21.06 2.28
21.56 1.36
21.66 0.56
21.64 -0.52
22.14 2.32
22.62 3.04
6.720
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