1396: 求和IV
[Creator : ]
Description
求-1/2-1/4-1/6……-1/n的值。（n为偶数且大于等于2，结果保留5位小数，结果后有一换行。提示：采用循环输入while(scanf()!=EOF)形式）
Input
20
50
100
500
1000
50
100
500
1000
Output
-1.46448
-1.90798
-2.24960
-3.05034
-3.39641
-1.90798
-2.24960
-3.05034
-3.39641
Sample Input Copy
20
50
100
500
1000
Sample Output Copy
-1.46448
-1.90798
-2.24960
-3.05034
-3.39641