#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef pair<int, int> ii;
typedef pair<ll, ll> l4;
#define pb push_back
#define mp make_pair

const int mod = 1e9+7;

ll k;
ll id(ll k)
{
  return (1+k)*k/2;
}
ll sum(ll id)
{
  return id*id;
}
int main()
{
  scanf("%lld", &k);
  printf("%lld\n", sum(id(k))-sum(id(k-1)));
}