POJ 1284 Primitive Roots 欧拉函数模板题

#include <algorithm>
#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <queue>
#include <cmath>
#include <stack>
#include <map>
#include <ctime>
#include <iomanip>

#pragma comment(linker, "/STACK:1024000000");
#define EPS (1e-6)
#define LL long long
#define ULL unsigned long long
#define _LL __int64
#define INF 0x3f3f3f3f
#define Mod 1000000007

using namespace std;

int p;
unsigned euler(unsigned x)
{
    unsigned i,res=x;
    for(i=2;i<(int)sqrt(x*1.0)+1;i++)
        if(x%i==0)
        {
            res=res/i*(i-1);
            while(x % i==0)
                x/=i;
        }
    if(x>1)
        res=res/x*(x-1);
    return res;
}
int main()
{
    while(scanf("%d",&p)!=EOF)
    {
        printf("%d\n",euler(p-1));
    }
    return 0;
}