筛法求欧拉函数（poj2478

求1～n的欧拉函数的值

#include <iostream>
#include <cstdio>
#include <queue>
#include <algorithm>
#include <cmath>
#include <cstring>
#define inf 2147483647
#define N 1000010
#define p(a) putchar(a)
#define For(i,a,b) for(long long i=a;i<=b;++i)
 
using namespace std;
long long n;
long long a[N];
void in(long long &x){
    long long y=;char c=getchar();x=;
    while(c<''||c>''){if(c=='-')y=-;c=getchar();}
    while(c<=''&&c>=''){ x=(x<<)+(x<<)+c-'';c=getchar();}
    x*=y;
}
void o(long long x){
    if(x<){p('-');x=-x;}
    if(x>)o(x/);
    p(x%+'');
}
 
int main(){
    a[]=;
    For(i,,1e6)
        if(!a[i])
            for(long long j=i;j<=1e6;j+=i){
                if(!a[j]) a[j]=j;
                a[j]=a[j]/i*(i-);
            }
    For(i,,1e6)
        a[i]+=a[i-];
    while(cin>>n&&n){
        o(a[n]-);p('\n');
    }
    return ;
}