#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES

#include "bits/stdc++.h"
using namespace std;
#define rep(i,n) for (int i=0;i<(n);++i)
#define rep2(i,a,b) for (int i=(a);i<(b);++i)
#define rrep(i,n) for (int i=(n)-1;i>=0;--i)
#define rrep2(i,a,b) for (int i=(a)-1;i>=b;--i)
#define chmax(a, b) (a = (a) < (b) ? (b) : (a))
#define chmin(a, b) (a = (a) > (b) ? (b) : (a))
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
#define all(a) begin(a),end(a)
#define ifnot(a) if(not (a))
#define dump(x)  cerr << #x << " = " << (x) << endl
// #define int ll
#ifdef _MSC_VER
const bool test = true;
#else 
const bool test = false;
#endif

int dx[] = { 1,0,-1,0 };
int dy[] = { 0,1,0,-1 };
const int INF = 1 << 28;
const ll INFL = (ll)1 << 58;
ll mod = (int)1e9 + 7;
const double eps = 1e-10;
typedef long double Real;
// return -1, 0, 1
int sgn(const Real& r) { return (r > eps) - (r < -eps); }
int sgn(const Real& a, const Real &b) { return sgn(a - b); }

//.....................
const int MAX = (int)2e5 + 5;

int H, W;

bool ng(int y, int x) {
	return y < 0 || H <= y || x < 0 || W <= x;
}

vector<string> split(const string &str, char sep){ 
	vector<string> v;
	stringstream ss(str);
	string buffer;
	while (getline(ss, buffer, sep)) {
		v.push_back(buffer);
	}
	return v;
}

ll N, K;

void solve() {
	cin >> N;
	cout << N * (N + 1) / 2 << endl;
}

signed main() {
	int T = 10;
	cout << fixed << setprecision(15);
	rep(i, T) {
		char s[MAX];
		if (scanf("%s", s) == EOF) break;
		int n = strlen(s);
		for (int i = n - 1; i > -1; i--) {
			ungetc(s[i], stdin);
		}
		solve();
	}
	return 0;
}