#include<bits/stdc++.h>
using namespace std;
int main(){
    int a[105];
    int s=0;
    int n;
    cin>>n;
    a[1]=1;
    a[2]=3;
    for(int i=3;i<=n;i++){
        a[i]=a[i-1]+i;
    }
    for(int i=1;i<=n;i++){
        s=s+a[i];
    }
    cout<<s;
    return  0;
}
/**************************************************************
	Problem: 1148
	User: luyanchen
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/