sgu102 Coprimes

102. Coprimes

time limit per test: 0.25 sec. 
memory limit per test: 4096 KB

For given integer N (1<=N<=10⁴) find amount of positive numbers not greater than N that coprime with N. Let us call two positive integers (say, A and B, for example) coprime if (and only if) their greatest common divisor is 1. (i.e. A and B are coprime iff gcd(A,B) = 1).

Input

Input file contains integer N.

Output

Write answer in output file.

Sample Input

9

Sample Output

6

题意：对于数N，求不大于N的正整数中，与N互质的数有多少个。

思路1：因为N的数值范围比较小，最简单的方法是使用枚举法，直接枚举所有不大于N的数，求gcd，统计个数。方法比较简便。这样要注意一个小小的bug，1和1也是互质的，因为他们的最大公约数是1。因为这个wa了两次T T。

思路2：用欧拉函数求解。