#include<bits/stdc++.h>
#include<algorithm>
#include<math.h>
#define pd
#define ll long long
using namespace std;
int main()
{
    int k;
    scanf("%d",&k);
    ll sum=0,i,x=0,n,ans=0;
    for(i=1;i<=k-1;i++)
    {
        x+=i;
    }
    n=x+k;
    sum=x*x;
    ans=n*n;
    ans=ans-sum;
    cout<<ans<<"\n";
}