#include <iostream>
#include <vector>
#include <string>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <algorithm>	// require sort next_permutation count __gcd reverse etc.
#include <cstdlib>	// require abs exit atof atoi 
#include <cstdio>		// require scanf printf
#include <functional>
#include <numeric>	// require accumulate
#include <cmath>		// require fabs
#include <climits>
#include <limits>
#include <cfloat>
#include <iomanip>	// require setw
#include <sstream>	// require stringstream 
#include <cstring>	// require memset
#include <cctype>		// require tolower, toupper
#include <fstream>	// require freopen
#include <ctime>		// require srand
#define rep(i,n) for(int i=0;i<(n);i++)
#define ALL(A) A.begin(), A.end()

using namespace std;

typedef long long ll;
typedef pair<int, int> P;

const int MAX_N = 10000;

int area[MAX_N+1];

void calc_area (void )
{
	memset (area, 0, sizeof (area ) );
	area[1] = 2;
	for (int i = 2; i <= MAX_N; i++ ){
		area[i] = i + area[i-1];
	} // end for
/*	
	rep (i, MAX_N + 1 )
		cerr << setw(6) << i << ": " << area[i] << endl;
*/
}

int main()
{
//	cut here before submit 
//	freopen ("testcase.area", "r", stdin );
	calc_area ();

	int n;
	while (scanf ("%d", &n ) != EOF ){
		cout << area[n] << endl;
	} // end loop
		
	return 0;
}