【2016-沈阳赛区网络赛-J】大素数模板（Count primes，uva 5901）

http://blog.csdn.net/chaiwenjun000/article/details/52589457

#include<bits/stdc++.h>
#define ll long long
using namespace std;
ll f[340000],g[340000],n;
void init(){
ll i,j,m;
for(m=1;m*m<=n;++m)f[m]=n/m-1;
for(i=1;i<=m;++i)g[i]=i-1;
for(i=2;i<=m;++i){
if(g[i]==g[i-1])continue;
for(j=1;j<=min(m-1,n/i/i);++j){
if(i*j<m)f[j]-=f[i*j]-g[i-1];
else f[j]-=g[n/i/j]-g[i-1];
}
for(j=m;j>=i*i;--j)g[j]-=g[j/i]-g[i-1];
}
}
int main(){
while(scanf("%I64d",&n)!=EOF){
init();
cout<<f[1]<<endl;
}
return 0;
}