# 直接模拟，好理解 ``` #include <bits/stdc++.h> using namespace std; int main(){ int n,k,sum=0; cin>>k; for(n=1;k-n>=0;k-=n++){ sum=sum+n*n; } cout<<sum+k*n; } ``` by lionrenard @ 2019-08-26 19:09:06