题解

#include <bits/stdc++.h>
using namespace std;
int main(){
int n,a,b,c;
a=b=c=0;
cin>>n;
do{
a++;
b+=a;
if(b<n)c+=a*a;
else c+=(n-(b-a))*a;
}while(b<n);
cout<<c;
return 0;
}