HUD 4473

比赛的时候看都没看到这道题，现在直接看题外加解题报告，感觉好简单啊

思维啊，思维啊，思维啊

#include<cstdio>#include<cmath>typedef long long ll;ll power3(ll n){ll ret=pow(n,1.0/3);while(ret*ret*ret<n)ret ++;while(ret*ret*ret>n)ret --;return ret;}ll power2(ll n,ll i){ll ret=pow(n/i,1.0/2);while(ret*ret*i<n)ret ++;while(ret*ret*i>n)ret --;return ret;}int main(){ll n,id=0;while(~scanf("%I64d",&n)){ll q3=power3(n);ll ans=q3;ll i,j,t;for(i=1;i<=q3;i++){t=n/(i*i);ans += (t-i)*3;ll q2=power2(n,i);ans += (q2-i)*3;for(j=i+1;j<=q2;j++){t=n/(i*j);ans += (t-j)*6;}}printf("Case %I64d: %I64d\n",++id,ans);}return 0;}