P2158 [SDOI2008]仪仗队

#include<iostream>
#include<cstdio>
#include<queue>
#include<algorithm>
#include<cmath>
#include<ctime>
#include<set>
#include<map>
#include<stack>
#include<cstring>
#define inf 2147483647
#define For(i,a,b) for(register int i=a;i<=b;i++)
#define p(a) putchar(a)
#define g() getchar()
//by war
//2017.11.3
using namespace std;
int n;
int ans;
int prime[40010];
bool vis[40010];
int cnt,tot;
int pr[40010];
void in(int &x)
{
    int y=1;
    char c=g();x=0;
    while(c<‘0‘||c>‘9‘)
    {
    if(c==‘-‘)
    y=-1;
    c=g();
    }
    while(c<=‘9‘&&c>=‘0‘)x=(x<<1)+(x<<3)+c-‘0‘,c=g();
    x*=y;
}
void o(int x)
{
    if(x<0)
    {
        p(‘-‘);
        x=-x;
    }
    if(x>9)o(x/10);
    p(x%10+‘0‘);
}

void Euler()
{
    For(i,2,n)
    {
        if(!vis[i])prime[++cnt]=i;
        for(register int j=1;j<=cnt&&i*prime[j]<=n;j++)
        {
            vis[i*prime[j]]=true;
            if(i%prime[j]==0)
            break;
        }
    }
}

int Eulerfunction(int x)
{
    tot=0;
    int c=x;
    For(i,1,cnt)
    {
        if(prime[i]>x)
        break;
        if(x%prime[i]==0)
        pr[++tot]=prime[i];    
    }
    For(i,1,tot)
    c=c-c/pr[i];
    return c;
}

int main()
{
    in(n);
    n--;
    Euler();
    For(i,1,n)
    ans+=Eulerfunction(i);
    o(ans*2+1);
     return 0;
}