#include<bits/stdc++.h>
using namespace std;
int main() {
int n,i=1,sum=0;
cin>>n;
while(n){
if(n<i){
sum+=n*i;
n-=n;
}else{
sum+=i*i;
n-=i;
}
i+=1;
cout<<sum;
return 0;
王子谦 LV 9
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