/*********** [ scopeInfinity ] ******************/
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef std::vector<ll> vll;
typedef std::vector<pair<int,int> > vpi;
typedef std::vector<pair<ll,ll> > vpl;
typedef std::vector<int> vi;

ll MOD = 1e9+7;
ll PRIME =  999727999;
ll PRIME2 = 999999937;
ll INF = LLONG_MAX/4;

#define forv(it,m) for (auto it = (m).begin(); it != (m).end(); ++it)
#define rep(i,n) for (int i=0;i<n;i++)
#define all(v) v.begin(),v.end()
#define endl '\n' 
#define mp make_pair
#define pb(x) push_back((x))
#define what_is(x) cerr << #x << " is " << (x) << endl;
#define NEW(x,n) {(x).clear();(x).resize((n));}
#define xx first
#define yy second

template <class F1,class F2> ostream& operator<<(ostream& os, const pair<F1,F2>& p) {
  return os<<p.xx<<' '<<p.yy; }
template <class F1,class F2> istream& operator>>(istream& is, pair<F1,F2>& p) {
  return is>>p.xx>>p.yy; }

vector<string> &split(const std::string &s, char delim, vector<string> &e) {
    stringstream ss(s);
    string item;
    while(getline(ss, item, delim))
        e.push_back(item);
    return e;
}


ll Pow(ll a ,ll b ,ll Mo){
    ll ans = 1;
    for (; b; b >>= 1, a = a * a % Mo)
        if (b&1) ans = ans * a % Mo;
    return ans;
}


ll nCr(ll n,ll r) {
    static ll MAXF = 1e6;
    static std::vector<ll> fact(MAXF,1);
    for (int i = 1; i < MAXF; ++i)  fact[i]=(fact[i-1]*i)%MOD;
    MAXF=0;
    return (fact[n]*Pow((fact[r]*fact[n-r])%MOD,MOD-2,MOD))%MOD;
}

vector<int> Zfunc(string &s) {
    int n=s.length();
    vector<int> z(n,0);
    for(int i=1,l=0,r=0;i<n;i++) {
        if(i<=r) 
            z[i] = min(z[i-l],r-i+1);
        while(i+z[i]<n && s[i+z[i]]==s[z[i]])
            z[i]++;
        if(r<i+z[i]-1)
            l=i,r=i+z[i]-1;
    }
    return z;
}

ll solve(ll x) {
	return x*(x+1)/2;

}

int main(int argc, char const *argv[])
{
	std::ios::sync_with_stdio(false);cin.tie(0);
	// cout<<fixed<<setprecision(1);
	ll k;
	cin>>k;
	ll b=k*(k+1)/2;
	ll a=k*(k-1)/2;
	ll s = solve(b)-solve(a);
	s = 2*s-k;
	cout<<s;
	

	return 0;
}