只看某一个象限 能看到的数 == 一个 象限*4+4

能看到的树既距离原点的距离 gcd(x,y)==1

a 和 b 一大一小 预处理2000以内的phi函数,枚举小的一条边

从1...a 与 a gcd 为 1 的数的个数就是 phi(a)

从 1+a ... 2*a 与 a gcd 为 1 的数的个数 因为 GCD(i,a) = GCD(i+a,a) 所以还是 phi(a)

....

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Description

Background

The saying ``You can't see the wood for the trees'' is not only a cliche, but is also incorrect. The real problem is that you can't see the trees for the wood. If you stand in the middle of a wood, the trees tend to obscure each other and the number of distinct trees you can actually see is quite small. This is especially true if the trees are planted in rows and columns, because they tend to line up. The purpose of this problem is to find how many distinct trees one can see if one were standing on the position of a tree in the middle of the wood.

The Problem

For a mathematically more precise description we assume that you are situated at the origin of a coordinate system in the plane.

Trees are planted at all positions , with "x|<=a and |y|<=b .

A tree at pZ??http://www.2cto.com/kf/ware/vc/" target="_blank" class="keylink">vc2l0aW9uICh4LHkpIGNhbiBiZSBzZWVuIGZyb20gdGhlIG9yaWdpbiBpZiB0aGVyZSBhcmUgbm8gb3RoZXIgdHJlZXMgb24gdGhlIHN0cmFpZ2h0IGxpbmUgZnJvbSAoMCwwKSB0byAoeCx5KSAuIEZpbmQgdGhlIG51bWJlciBLIG9mIGFsbCB0aGUgdHJlZXMgaW4gdGhlIHdvb2QgdGhhdCBjYW4gYmUgc2VlbiBmcm9tIHRoZSBvcmlnaW4gYW5kIHRoZSBudW1iZXIgTiBvZiBhbGwgdGhlIHRyZWVzIHRvCiBjb21wdXRlIHRoZSBmcmFjdGlvbiA8aW1nIHNyYz0="https://www.cppentry.com/upload_files/article/49/1_gbrpy__.gif" width="19" height="29" id="_x0000_i1027" align="top" border="0" alt="\">.

Hint: The Euler phi function is defined to be the number of integers m in the range 1≤m≤n relatively prime to n :

Instead of counting (an adequate method for small n !) you could as well use the following identity:

Hint: Remember that gcd (m,n)= gcd (m+n,n)= gcd (m+2n,n)= gcd (m+in,i)

You might be surprised that the fraction converges to 0.607927 for an infinitely large wood.

The Input

Each scenario consists of a line with the two numbers a and b (separated by a white space), with 1 <= a <= 2000 and 1 <= b <= 2000000 Input is terminated by a line with two zeros.

The Output

For each scenario print a line containing the fraction with a precision of 7 digits after the decimal point. Error less than 2e-7 or 2*10^(-7) will be tolerated.

Sample Input

3 2
0 0

Sample Output

Source

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/* ***********************************************
Author        :CKboss
Created Time  :2015年02月03日 星期二 22时13分33秒
File Name     :UVA10214.cpp
************************************************ */

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