bzoj2190: [SDOI2008]仪仗队

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
#define rep(i,s,t) for(int i=s;i<=t;i++)
#define clr(x,c) memset(x,c,sizeof(x))
const int nmax=40005;
int phi[nmax],prime[nmax];bool vis[nmax];
void init(){
    phi[1]=1;int cnt=0;
    rep(i,2,nmax-1){
        if(!vis[i]) prime[++cnt]=i,phi[i]=i-1;
        rep(j,1,cnt){
            int x=prime[j];
            if(i*x>=nmax) break;
            vis[i*x]=1;
            if(i%x==0) {
                phi[i*x]=phi[i]*x;break;
            }else phi[i*x]=phi[i]*phi[x];
        }
    }
    //rep(i,1,100) printf("%d ",phi[i]);printf("\n");
}
int main(){
    init();
    int ans=0,n;scanf("%d",&n);
    rep(i,1,n-1) ans+=phi[i];
    printf("%d\n",ans*2+1);
    return 0;
}