SGU 102（Coprimes）

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

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题意：计算小于n。并且与n互质的数

欧拉函数问题（详情参见http://blog.csdn.net/qq_21120027/article/details/47863587）

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#include<iostream>#include <cstdio>#include <vector>#include <string.h>#include <math.h>#define N 10010using namespace std;vector<int> prime;int flag[N];void PRIME(){    int i, j;    memset(flag, 1, sizeof(flag));    flag[1] = 0;    flag[2] = 1;    for (i = 3; i < N; i++)    {        for (j = 2; flag[i] && j * i< N; j++)        {            flag[j*i] = 0;        }    }    /*for (i = 1; i < N; i++)    {        if (flag[i])        {            prime.push_back(i);        }    }*/}int gcd(int a, int b){    if (b == 0)    {        return a;    }    return gcd(b, a%b);}int main(){#ifndef  ONLINE_JUDGE    //freopen("1.txt", "r", stdin);#endif    PRIME();    int n, ans, i;    while(~scanf("%d", &n))    {        if (n == 1)         {            cout << "1\n";            continue;        }        if (flag[n])        {            cout << n-1 << endl;            continue;        }        ans = 0;        for (i = 1; i < n; i++)        {            if (gcd(n, i) == 1)            {                ans++;            }        }        cout << ans << endl;    }    return 0;}