洛谷 P1403 [AHOI2005]约数研究 (整除分块)

#include<iostream>
#include<algorithm>
#include<string.h>
#include<string>
#include<vector>
#include<cstdio>
#include<queue>
#include<map>
#include<set>
#include<math.h>
using namespace std;
const int inf=0x3f3f3f3f;
const int maxn=1e5+5;
typedef long long ll;
int dir[4][2]={-1,0,1,0,0,-1,0,1};
int main(){
    ios::sync_with_stdio(false);
    ll n;
    while(cin>>n){
       ll ans=0;
          for(ll x=1,y;x<=n;x=y+1){
                y=n/(n/x);
                ans+=n/x*(y-x+1);
          } 
          cout<<ans<<endl;
    }
}