代码:
#include<bits/stdc++.h>
using namespace std;
#define MAXN 10002
int main()
{
int n,i=1;
int k = 1;
cin>>n;
unsigned long long ans = 0;
while(k<=n)
{
for(int j=1; j<=i; j++)
{
ans += i;
k++;
if(k>n)
{
break;
}
}
i++;
}
cout<<ans<<endl;
return 0;
}